Stimulation with utilization of non-selected electrode

ABSTRACT

This disclosure describes techniques that support delivering electrical stimulation current via at least two user-selected electrodes of an implantable medical device (IMD) and automatically delivering balancing current below via at least one non-selected electrode. Balancing currents delivered via the at least one non-selected electrode may be configured with an amplitude below a perception threshold of a patient. Delivery of balancing current via the at least one third electrode may allow an implantable medical device to automatically balance the total current delivered to a patient.

TECHNICAL FIELD

The disclosure relates to medical devices and, more particularly, tomedical devices that deliver electrical stimulation therapy.

BACKGROUND

Medical devices may be used to treat a variety of medical conditions.Medical electrical stimulation devices, for example, may deliverelectrical stimulation therapy to a patient via implanted electrodes.Electrical stimulation therapy may include stimulation of nerve, muscle,or brain tissue, or other tissue within a patient. An electricalstimulation device may be fully implanted within the patient. Forexample, an electrical stimulation device may include an implantableelectrical stimulation generator and one or more implantable leadscarrying electrodes. Alternatively, the electrical stimulation devicemay comprise a leadless stimulator. In some cases, implantableelectrodes may be coupled to an external electrical stimulationgenerator via one or more percutaneous leads or fully implanted leads.

Medical electrical stimulators may be used to deliver electricalstimulation therapy to patients to relieve a variety of symptoms orconditions such as chronic pain, tremor, Parkinson's disease,depression, epilepsy, urinary or fecal incontinence, pelvic pain, sexualdysfunction, obesity, or gastroparesis. An electrical stimulator may beconfigured to deliver electrical stimulation therapy via leads thatinclude electrodes implantable proximate to the spinal cord, pelvicnerves, gastrointestinal organs, peripheral nerves, or within the brainof a patient. Stimulation proximate the spinal cord and within the brainare often referred to as spinal cord stimulation (SCS) and deep brainstimulation (DBS), respectively.

A clinician selects values for a number of programmable stimulationparameters in order to define the electrical stimulation therapy to bedelivered to a patient. For example, the clinician may select a currentor voltage amplitude of the stimulation, and various characteristics ofthe stimulation waveform. In addition, the clinician may specify anelectrode configuration used to deliver stimulation, including selectedelectrode combinations and electrode polarities. If the stimulation isdelivered in the form of pulses, for example, the clinician may specifya current or voltage pulse amplitude, pulse width and pulse rate. A setof parameter values may be referred to as a stimulation program. Aprogram group may include multiple programs. Multiple programs in aprogram group may be delivered on a simultaneous, time-interleaved, oroverlapping basis.

SUMMARY

In general, this disclosure describes techniques for substantiallysimultaneously delivering electrical stimulation via at least oneelectrode on an implantable medical device (IMD) housing and two or moreelectrodes on one or more leads coupled to the housing. At least one ofthe lead electrodes has the same polarity as an electrode on the housingof the IMD. The techniques may allow a user to transition between astimulation setting that uses a unipolar electrode arrangement to astimulation setting that uses a bipolar electrode arrangement, andpermit a range of hybrid electrode arrangements that make use of variouscombinations of unipolar and bipolar relationships between theelectrodes. For convenience, a hybrid stimulation arrangement thatcombines both unipolar and bipolar electrode relationships also may bereferred to as an omnipolar arrangement.

This disclosure also describes techniques that support balancingstimulation currents delivered by two or more electrodes on one or moreleads as described above with sub-threshold electrical currentsdelivered via one or more lead electrodes, or other electrodes locatedin the body, configured to deliver balancing current. It may bedesirable for the balancing currents according to this technique to bedelivered by sub-threshold electrodes, i.e., electrodes that deliverenergy (e.g., current, voltage) at amplitude levels below a threshold atwhich stimulation can be perceived by a patient.

In one example, the disclosure provides a method. The method includesreceiving, via a user interface of a programmer device for animplantable electrical stimulator, user input specifying at least onefirst user-selected electrode to deliver electrical stimulation of afirst polarity and at least one second user-selected electrode todeliver electrical stimulation of a second polarity different than thefirst polarity for delivery of electrical stimulation from animplantable electrical stimulator to a patient. The method furtherincludes receiving, via the user interface, user input specifyingamounts of electrical stimulation current to be supplied via the atleast one first user-selected electrode and the at least one seconduser-selected electrode. The method further includes automaticallyselecting at least one third electrode not specified as a user-selectedelectrode to deliver electrical stimulation to substantially balance theelectrical stimulation current to be delivered via the at least onefirst user-selected electrode and the at least one second user-selectedelectrode. The method further includes defining a program to controldelivery of the electrical stimulation by the stimulator based on theuser input.

In another example, the disclosure provides a computer-readable storagemedium comprising instructions. The instructions cause a processor toreceive, via a user interface of a programmer device for an implantableelectrical stimulator, user input specifying at least one firstuser-selected electrode to deliver electrical stimulation of a firstpolarity and at least one second user-selected electrode to deliverelectrical stimulation of a second polarity different than the firstpolarity for delivery of electrical stimulation from an implantableelectrical stimulator to a patient. The instructions further cause theprocessor to receive, via the user interface, user input specifyingamounts of electrical stimulation current to be supplied via the atleast one first user-selected electrode and the at least one seconduser-selected electrode. The instructions further cause the processor toautomatically select at least one non user-selected third electrode todeliver electrical stimulation to substantially balance the electricalstimulation delivered by the at least one first user-selected electrodeand the at least one second user-selected electrode. The instructionsfurther cause the processor to define a program to control delivery ofthe electrical stimulation by the stimulator based on the user input.

In another example, the disclosure provides a device. The deviceincludes means for receiving, via a user interface of a programmerdevice for an implantable electrical stimulator, user input specifyingat least one first user-selected electrode to deliver electricalstimulation of a first polarity and at least one second user-selectedelectrode to deliver electrical stimulation of a second polaritydifferent than the first polarity for delivery of electrical stimulationfrom an implantable electrical stimulator to a patient. The devicefurther includes means for receiving, via the user interface, user inputspecifying amounts of electrical stimulation current to be supplied viathe at least one first user-selected electrode and the at least onesecond user-selected electrode. The device further includes means forautomatically selecting at least one third electrode to deliverelectrical stimulation to substantially balance electrical stimulationdelivered by the at least one first user-selected electrode and the atleast one second user-selected electrode. The device further includesmeans for defining a program to control delivery of the electricalstimulation by the stimulator based on the user input. In anotherexample, this disclosure provides a device. The device includes aprogrammer for an implantable electrical stimulator. The programmerincludes a user interface that receives user input specifying at leastone first user-selected electrode to deliver electrical stimulation of afirst polarity and at least one second user-selected electrode todeliver electrical stimulation of a second polarity different than thefirst polarity for delivery of electrical stimulation from animplantable electrical stimulator to a patient, wherein the userinterface further receives user input specifying amounts of electricalstimulation current to be supplied via the at least one firstuser-selected electrode and the at least one second user-selectedelectrode. The programmer further includes a processor thatautomatically selects at least one non user-selected third electrode todeliver electrical stimulation to substantially balance the electricalstimulation delivered by the at least one first user-selected electrodeand the at least one second user-selected electrode, wherein theprocessor defines a program to control delivery of the electricalstimulation by the implantable electrical stimulator based on the userinput.

In another example, the disclosure provides a system. The systemincludes an implantable electrical stimulator and a programmer. Theprogrammer includes a user interface that receives, via a user interfaceof a programmer device for an implantable electrical stimulator, userinput specifying at least one first user-selected electrode to deliverelectrical stimulation of a first polarity and at least one seconduser-selected electrode to deliver electrical stimulation of a secondpolarity different than the first polarity for delivery of electricalstimulation from an implantable electrical stimulator to a patient. Theuser interface further receives, via the user interface, user inputspecifying amounts of electrical stimulation current to be supplied viathe at least one first user-selected electrode and the at least onesecond user-selected electrode. The programmer automatically selects atleast one third electrode to deliver electrical stimulation tosubstantially balance electrical stimulation delivered by the at leastone first user-selected electrode and the at least one seconduser-selected electrode. The programmer further includes a processorthat defines a program to control delivery of the electrical stimulationby the stimulator based on the user input.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example therapy systemthat includes an implantable stimulator coupled to a stimulation lead.

FIG. 2 is a conceptual diagram illustrating another example therapysystem that includes an implantable stimulator coupled to a stimulationlead.

FIG. 3 is a block diagram illustrating various example components of animplantable electrical stimulator.

FIG. 4 is a block diagram illustrating various example components of anexternal programmer for use with an electrical stimulator.

FIG. 5 is a block diagram illustrating various components of an exampleelectrical stimulation generator for use in the implantable electricalstimulator of FIG. 3.

FIG. 6 is a block diagram illustrating the example stimulation generatorof FIG. 5 in greater detail.

FIGS. 7 and 8 are circuit diagrams illustrating example circuitry foruse in the stimulator generator shown in FIG. 5.

FIGS. 9A-9B are conceptual diagrams illustrating example leads andelectrode configurations that may be used for delivering electricalstimulation therapy as described in this disclosure.

FIG. 10 is a conceptual diagram illustrating an example paddle lead thatmay be used for delivering electrical stimulation therapy as describedin this disclosure.

FIG. 11 is conceptual diagram illustrating a stimulation field that maybe produced using a bipolar stimulation arrangement.

FIG. 12 is conceptual diagram illustrating a unipolar stimulationarrangement that may be produced using a unipolar stimulationarrangement.

FIGS. 13-16 are conceptual diagrams illustrating various omnipolarstimulation arrangements that may be produced using the techniques ofthis disclosure.

FIG. 17 is a flow diagram illustrating an example method of deliveringelectrical stimulation using the techniques of this disclosure.

FIGS. 18-22 are schematic diagrams illustrating example user interfacespresented by the programmer of FIG. 4.

FIG. 23 is a schematic illustrating an example electrode contributiondetermination.

FIGS. 24-26 are schematic diagrams illustrating example user interfacespresented by the programmer of FIG. 4.

FIG. 27 is a flow diagram illustrating example operation of theprogrammer for generating a program to control delivery of electricalstimulation.

FIG. 28 is a flow diagram illustrating another example operation of theprogrammer for generating a program to control delivery of electricalstimulation.

FIG. 29 is a flow diagram illustrating example operation of theprogrammer for transitioning from a unipolar stimulation arrangement toa hybrid stimulation arrangement, and finally to a bipolar or multipolarstimulation arrangement.

FIGS. 30-32 are conceptual diagrams illustrating example lead andelectrode configurations that may be used for delivering electricalstimulation therapy using sub-threshold electrodes according to varioustechniques of this disclosure.

FIGS. 33-36 are schematic diagrams illustrating example user interfacespresented by the programmer of FIG. 4.

FIG. 37 is a flow diagram illustrating example operation of a programmerfor generating a program to control delivery of electrical stimulation.

FIG. 38 is a flow diagram illustrating an example method of deliveringelectrical stimulation using the techniques of this disclosure.

FIG. 39 is a flow diagram illustrating another example operation of theprogrammer for generating a program to control delivery of electricalstimulation.

DETAILED DESCRIPTION

This disclosure describes techniques that support delivering electricalstimulation having a first polarity via an electrode on a housing of animplantable medical device (IMD) while substantially simultaneouslydelivering electrical stimulation having the first polarity via one ormore electrodes on one or more leads engaged to the IMD, in conjunctionwith one or more electrodes delivering electrical stimulation having asecond polarity opposite the first polarity on the one or more leads.The housing of the IMD alternatively may be referred to as a case orcan. The stimulation may be constant current-based or constantvoltage-based stimulation in the form of pulses or continuous waveforms.Delivery of stimulation via both a housing anode and one or more leadanodes, for example, may allow a user to control current paths betweenthe housing electrode and the lead electrode(s) in a relative manner toachieve different electric stimulation field shapes.

A unipolar stimulation arrangement generally refers to the use of ananode on the housing that sources current and one or more cathodes onone or more leads that sink current. A bipolar stimulation arrangementgenerally refers to the use of an anode on a lead that sources currentand a cathode on the same lead and/or another lead that sink current. Amultipolar stimulation arrangement generally refers to the use of morethan one anode on a lead that each source current and one or morecathodes on the same lead or another lead that sink current, or the useof one anode on a lead that sources current and multiple cathodes on thesame lead or another lead that sink current.

A unipolar stimulation arrangement may offer some advantages over abipolar stimulation arrangement. For instance, a unipolar stimulationarrangement may present less impedance than a bipolar stimulationarrangement and, as a result, may consume less power than a bipolarstimulation arrangement. In a bipolar stimulation arrangement using twoleads, for example, electrical stimulation current sourced through ananode on one lead may return through a cathode on the other lead. As anillustration, if each lead has an impedance of about 200 ohms, asignificant energy can be lost in the circuit due to impedance loadingof the stimulation current. In contrast, in a unipolar arrangement,electrical stimulation current sourced through an anode on the canreturns via a cathode on a 200 ohm lead after being transmitted throughtissue. In some cases, the impedance of tissue is significantly lowerthan that of a lead. As such, less energy is lost in the unipolarstimulation arrangement.

However, in other instances, a bipolar stimulation arrangement may offeradvantages over a unipolar stimulation arrangement. For instance, usinga unipolar stimulation arrangement, the electric stimulation fieldcreated between the housing anode and the lead cathode may be shapedlike a sphere as a result of the distance between the two (or more)electrodes. The stimulation provided to a patient by the largesphere-like stimulation field may be less desirable to a patient thanother, more localized fields. For instance, the volume of tissueactivation may be greater using a unipolar stimulation arrangement,which may result in additional, undesired, tissue being stimulated. Incontrast, a bipolar stimulation arrangement, with the anodes andcathodes on one or more leads, may provide stimulation fields that aresmaller and have more localized shapes (due to the close proximitybetween the anodes and cathodes on leads) than the sphere-like fieldcreated by a unipolar stimulation arrangement. A lead-based anode inproximity to a lead-based cathode may provide a shield-like effect thatpermits the generation of a more localized field that is concentrated ontarget tissue, avoiding activation of other tissue.

Techniques of this disclosure support combining attributes of both theunipolar stimulation arrangement and the bipolar stimulation arrangementto provide a hybrid arrangement that may be referred to as an omnipolararrangement. By providing at least one housing anode and one or moreanodes on one or more leads, and delivering electrical stimulation viathe housing anode and the one or more anodes on the leads substantiallysimultaneously, in conjunction with one or more lead-based cathodes, thetechniques of this disclosure may offer one or more advantages.

For example, an IMD using such a configuration may consume less powerthan a bipolar stimulation arrangement would alone, yet provide moreflexibility relative to a unipolar arrangement in shaping a stimulationfield created by the stimulation current delivered by the housing anodeand the lead anode. In addition, these techniques may allow more precisesteering, shaping or focusing of an electric field to transition betweena unipolar stimulation arrangement to a bipolar stimulation arrangement.The user may select a balance between delivery of stimulation via aunipolar stimulation arrangement and delivery of stimulation via atleast one lead anode.

In some cases, delivery of stimulation may be transitioned from unipolarto bipolar (or multipolar), using different weighted omnipolarcombinations of unipolar vs. bipolar (or multipolar) until the userselects one of the omnipolar combinations, e.g., based on the user'sperceived efficacy of the omnipolar combination. This transitioningfeature may allow more flexibility in selecting the relative strengthsof the stimulation delivered by anodes on the housing and the lead. Insome cases, one or more anodes disposed on one or more leads near one ormore cathodes carried by the leads may provide a shield effect that moreeffectively localizes, confines, or concentrates electrical stimulationin the vicinity of the cathodes. Different weighted combinations ofstimulation delivered via housing and lead anodes can determine theshield strength.

This disclosure also describes techniques that support automaticallybalancing stimulation currents delivered by two or more user selectedelectrodes on one or more leads as described above by one or morenon-user selected lead electrodes, or other electrodes located in thebody, configured to deliver balancing current. It may be desirable forthe balancing current to be delivered by sub-threshold electrodes, i.e.,electrodes that deliver energy (e.g., current, voltage) at amplitudelevels below a threshold at which stimulation can be perceived by apatient. It may be desirable to maintain a charge density of energydelivered by the sub-threshold electrodes at a lower level than a chargedensity of energy delivered at or above a threshold in which stimulationmay be perceived by the patient. It may further or instead be desirableto deliver balancing energy via one or more electrodes distal from thetwo or more user selected electrodes.

As used throughout this disclosure, substantially simultaneous deliveryof stimulation, whether current or voltage, refers to the partial orcomplete time-wise synchronization of the electrical stimulation pulsesor waveforms. Complete time-wise synchronization may refer to thehousing electrode, e.g., anode, delivering stimulation at the same timethat one or more lead electrodes, e.g., anodes, deliver stimulation. Forexample, complete time-wise synchronization may include the rising edgeof the stimulation pulse or waveform being delivered by the housingelectrode, e.g., anode, substantially coinciding with the rising edge ofthe stimulation pulse or waveform being delivered by the one or morelead electrodes, e.g., anodes, and the falling edge of the stimulationpulse or waveform being delivered by the housing electrode, e.g., anode,coinciding with the falling edge of the stimulation pulse or waveformbeing delivered by the one or more lead electrodes, e.g., anodes.Complete time-wise synchronization may also include a pulse delivered bya housing anode, for example, being delivered within the pulse width ofa pulse delivered by a lead anode, for example. Partial time-wisesynchronization may refer to the housing electrode, e.g., anode,delivering one electrical stimulation pulse or waveform while at leastone lead electrode, e.g., anode, is delivering another electricalstimulation pulse or waveform such that at least a portion of one of therising or falling edge of one pulse or waveform overlaps in time with atleast a portion of one of the rising or falling edge of at least oneother pulse or waveform.

FIG. 1 is a conceptual diagram illustrating an example system 2 that maybe used to deliver stimulation therapy to patient 6. Patient 6ordinarily, but not necessarily, will be a human. Generally, therapysystem 2 includes implantable stimulator 4 that delivers electricalstimulation to patient 6 via one or more implantable electrodes (notshown). The implantable electrodes may be deployed on one or moreimplantable medical leads, such as implantable medical lead 10, and insome cases on a can electrode. The electrical stimulation may be in theform of constant current or voltage pulses or substantially continuouswaveforms. Various parameters of the pulses or waveforms may be definedby a stimulation program. The pulses or waveforms may be deliveredsubstantially continuously or in bursts, segments, or patterns, and maybe delivered alone or in combination with pulses or waveforms defined byone or more other stimulation programs. Although FIG. 1 shows a fullyimplantable stimulator 4, techniques described in this disclosure may beapplied to external stimulators having electrodes deployed viapercutaneously implantable leads. One or more of the electrodes may belocated on a housing 14, i.e., “can” or “case,” of the implantablestimulator 4. In addition, in some cases, implantable electrodes may bedeployed on a leadless stimulator.

In the example illustrated in FIG. 1, implantable stimulator 4 isimplanted within a subcutaneous pocket in a clavicle region of patient6. Stimulator 4 generates programmable electrical stimulation, e.g., acurrent waveform or current pulses, and delivers the stimulation via animplantable medical lead 10 carrying an array of implantable stimulationelectrodes 11. In some cases, multiple implantable leads may beprovided. In the example of FIG. 1, a distal end of lead 10 isbifurcated and includes two lead segments 12A and 12B (collectively“lead segments 12”). Lead segments 12A and 12B each include a set ofelectrodes forming part of the array of electrodes 11. In variousexamples, lead segments 12A and 12B may each carry four, eight, orsixteen electrodes. In FIG. 1, each lead segment 12A, 12B carries fourelectrodes, configured as ring electrodes at different axial positionsnear the distal ends of the lead segments. Throughout the remainder ofthis disclosure, for purposes of simplicity, the disclosure maygenerally refer to electrodes carried on “leads” rather than “leadsegments.”

FIG. 1 further depicts a housing, or can, electrode 13 carried byhousing 14. Housing electrode 13 may be formed integrally with an outersurface of hermetically-sealed housing 14 of implantable stimulator 4,also referred to in this disclosure as implantable medical device (IMD)4, or otherwise coupled to housing 14. In one example, housing electrode13 may be described as an active, non-detachable electrode on thesurface of the IMD. In some examples, housing electrode 13 is defined byan uninsulated portion of an outward facing portion of housing 14 of IMD4. Other divisions between insulated and uninsulated portions of housing14 may be employed to define two or more housing electrodes, which maybe referred to as case or can electrodes. In some examples, housingelectrode 13 comprises substantially all of housing 14, one side ofhousing 14, a portion of the housing 14, or multiple portions of housing14. In other examples, housing electrode 13 may be formed integrallywith header 8. For example, header 8 may comprise a conductive surfacethat functions as housing electrode 13. In example configurations inwhich header 8 functions as housing electrode 13, all of header 8 maycomprise a conductive surface, a portion of header 8 may comprise aconductive surface, or multiple portions of header 8 may compriseconductive surfaces. In one example implementation of the techniques ofthis disclosure, e.g., an omnipolar arrangement, one or more electrodes11 may transfer stimulation pulses from the lead 10 to the tissuesubstantially simultaneously with stimulation pulses delivered viahousing electrode 13.

In some examples, lead 10 may also carry one or more sense electrodes topermit implantable stimulator 4 to sense electrical signals from patient6. Some of the stimulation electrodes may be coupled to function asstimulation electrodes and sense electrodes on a selective basis. Inother examples, implantable stimulator 4 may be coupled to one or moreleads which may or may not be bifurcated. In such examples, the leadsmay be coupled to implantable stimulator 4 via a common lead extensionor via separate lead extensions.

A proximal end of lead 10 may be both electrically and mechanicallycoupled to header 8 on implantable stimulator 4 either directly orindirectly via a lead extension. Conductors in the lead body mayelectrically connect stimulation electrodes located on lead segments 12to implantable stimulator 4. Lead 10 traverses from the implant site ofimplantable stimulator 4 along the neck of patient 6 to cranium 18 ofpatient 6 to access brain 16. Lead segments 12A and 12B are implantedwithin the right and left hemispheres, respectively, in order to deliverelectrical stimulation to one more regions of brain 16, which may beselected based on the patient condition or disorder.

Implantable stimulator 4 may deliver, for example, deep brainstimulation (DBS) or cortical stimulation (CS) therapy to patient 6 viathe electrodes carried by, i.e., located on, lead segments 12 to treatany of a variety of neurological disorders or diseases. Exampleneurological disorders may include depression, dementia,obsessive-compulsive disorder and movement disorders, such asParkinson's disease, spasticity, epilepsy, and dystonia. DBS also may beuseful for treating other patient conditions, such as migraines andobesity. However, the disclosure is not limited to the configuration oflead 10 shown in FIG. 1, or to the delivery of DBS or CS therapy.

Lead segments 12A, 12B may be implanted within a desired location ofbrain 16 through respective holes in cranium 18. Lead segments 12A, 12Bmay be placed at any location within brain 16 such that the electrodeslocated on lead segments 12A, 12B are capable of providing electricalstimulation to targeted tissue during treatment. Example locations forlead segments 12A, 12B within brain 26 may include the pedunculopontinenucleus (PPN), thalamus, basal ganglia structures (e.g., globuspallidus, substantia nigra, subthalmic nucleus), zona inserta, fibertracts, lenticular fasciculus (and branches thereof), ansa lenticularis,and/or the Field of Forel (thalamic fasciculus). In the case ofmigraines, lead segments 12 may be implanted to provide stimulation tothe visual cortex of brain 16 in order to reduce or eliminate migraineheadaches afflicting patient 6. However, the target therapy deliverysite may depend upon the patient condition or disorder being treated.

The electrodes of lead segments 12A, 12B are shown as ring electrodes.Ring electrodes are commonly used in DBS applications because they aresimple to program and are capable of delivering an electrical field toany tissue adjacent to lead segments 12A, 12B. In other implementations,the electrodes of lead segments 12A, 12B may have differentconfigurations. For example, the electrodes of lead segments 12A, 12Bmay have a complex electrode array geometry that is capable of producingshaped electrical fields. The complex electrode array geometry mayinclude multiple electrodes (e.g., partial ring or segmented electrodes)around the perimeter of each lead segments 12A, 12B, rather than onering electrode. In this manner, electrical stimulation may be directedin a specific direction from lead segments 12 to enhance therapyefficacy and reduce possible adverse side effects from stimulating alarge volume of tissue. In alternative examples, lead segments 12 mayhave shapes other than elongated cylinders as shown in FIG. 1. Forexample, lead segments 12 may be paddle leads, spherical leads, bendableleads, or any other type of shape effective in treating patient 6.

Therapy system 2 also may include a clinician programmer 20 and/or apatient programmer 22. Clinician programmer 20 may be a handheldcomputing device that permits a clinician to program stimulation therapyfor patient 6 via a user interface, e.g., using input keys and adisplay. For example, using clinician programmer 20, the clinician mayspecify stimulation parameters, i.e., create programs, for use indelivery of stimulation therapy. Clinician programmer 20 may supporttelemetry (e.g., radio frequency (RF) telemetry) with implantablestimulator 4 to download programs and, optionally, upload operational orphysiological data stored by implantable stimulator 4. In this manner,the clinician may periodically interrogate implantable stimulator 4 toevaluate efficacy and, if necessary, modify the programs or create newprograms. In some examples, clinician programmer 20 transmits programsto patient programmer 22 in addition to or instead of implantablestimulator 4.

Like clinician programmer 20, patient programmer 22 may be a handheldcomputing device. Patient programmer 22 may also include a display andinput keys to allow patient 6 to interact with patient programmer 22 andimplantable stimulator 4. In this manner, patient programmer 22 providespatient 6 with a user interface for control of the stimulation therapydelivered by implantable stimulator 4. For example, patient 6 may usepatient programmer 22 to start, stop or adjust electrical stimulationtherapy. In particular, patient programmer 22 may permit patient 6 toadjust stimulation parameters of a program such as duration, current orvoltage amplitude, pulse width and pulse rate. Patient 6 may also selecta program, e.g., from among a plurality of stored programs, as thepresent program to control delivery of stimulation by implantablestimulator 4.

In some examples, implantable stimulator 4 delivers stimulationaccording to a group of programs at a given time. Each program of such aprogram group may include respective values for each of a plurality oftherapy parameters, such as respective values for each of current orvoltage amplitude, pulse width, pulse shape, pulse rate and electrodeconfiguration (e.g., electrode combination and polarity). Implantablestimulator 4 may interleave pulses or other signals according to thedifferent programs of a program group, e.g., cycle through the programs,to simultaneously treat different symptoms or different body regions, orprovide a combined therapeutic effect. In such examples, clinicianprogrammer 20 may be used to create programs, and assemble the programsinto program groups. Patient programmer 22 may be used to adjuststimulation parameters of one or more programs of a program group, andselect a program group, e.g., from among a plurality of stored programgroups, as the current program group to control delivery of stimulationby implantable stimulator 4.

Implantable stimulator 4, clinician programmer 20, and patientprogrammer 22 may communicate via cables or a wireless communication, asshown in FIG. 1. Clinician programmer 20 and patient programmer 22 may,for example, communicate via wireless communication with implantablestimulator 4 using RF telemetry techniques known in the art. Clinicianprogrammer 20 and patient programmer 22 also may communicate with eachother using any of a variety of local wireless communication techniques,such as RF communication according to the 802.11 or Bluetoothspecification sets, infrared communication, e.g., according to the IrDAstandard, or other standard or proprietary telemetry protocols. Each ofclinician programmer 20 and patient programmer 22 may include atransceiver to permit bi-directional communication with implantablestimulator 4.

Generally, system 2 delivers stimulation therapy to patient 6 in theform of constant current or voltage waveforms or constant current orvoltage pulses. The shapes of the pulses may vary according to differentdesign objectives. In the case of current-based stimulation, implantablestimulator 4 regulates current that is sourced or sunk by one or moreelectrodes, referred to as regulated electrodes. In some examples, oneof the electrodes may be unregulated. In such configurations, either thehousing electrode or a lead electrode may be the unregulated electrode.

A source current, i.e, an anodal current, may refer to a positivecurrent, i.e., a current having a positive polarity, that flows out ofan electrode, e.g., from a regulated current source via a regulatedcurrent path to surrounding tissue, or from a reference voltage via anunregulated current path. A sink current, i.e, a cathodal current, mayrefer to a negative current, i.e., a current having a negative polarity,that flows into an electrode, e.g. from surrounding tissue and is sunkby a regulated current sink via a regulated current path or by areference voltage via an unregulated current path. Regulated sourcecurrents may sum to produce a greater overall source current. Regulatedsink currents may sum to produce a greater overall sink current.Regulated source and regulated sink currents may partially or entirelycancel one another, producing a net difference in the form of a netsource current or sink current in the case of partial cancellation. Anunregulated current path can source or sink current approximately equalto this net difference.

As mentioned above, using the techniques of this disclosure, one or moreelectrodes 11 may transfer stimulation pulses from the lead 10 to thetissue substantially simultaneously with stimulation pulses deliveredvia housing electrode 13. For example, housing electrode 13 and one ormore electrodes 11 may be configured to act as anodes and sourcecurrent. Substantially simultaneously delivering stimulation via both ahousing anode and one or more lead anodes may allow a user to achievedifferent electric field shapes by controlling current paths between thehousing anode and the lead anode(s) in a relative manner.

FIG. 2 is a conceptual diagram illustrating system 30 that deliversstimulation therapy to spinal cord 38 of patient 36. Hence, like FIG. 1,FIG. 2 represents another example of an electrical stimulation systemthat may support omnipolar stimulation techniques described in thisdisclosure. Other electrical stimulation systems may be configured todeliver electrical stimulation to gastrointestinal organs, pelvic nervesor muscle, peripheral nerves, or other stimulation sites. In the exampleof FIG. 2, system 30 delivers stimulation therapy from implantablestimulator 34 to spinal cord 38 via one or more electrodes (not shown)carried by, i.e., located on, implantable medical leads 32A and 32B(collectively “leads 32”) as well as the housing of implantablestimulator 34, e.g., housing electrode 37. System 30 and, moreparticularly, implantable stimulator 34 may operate in a manner similarto implantable stimulator 4 (FIG. 1). That is, in a current-basedexample, implantable stimulator 34 delivers controlled currentstimulation pulses or waveforms to patient 36 via one or more regulated,stimulation electrodes. Alternatively, implantable stimulator 34 may beconfigured to deliver constant voltage pulses. As mentioned above, insome examples, one of the electrodes may be unregulated.

In the example of FIG. 2, the distal ends of leads 32 carry electrodesthat are placed adjacent to the target tissue of spinal cord 38. Theproximal ends of leads 32 may be both electrically and mechanicallycoupled to implantable stimulator 4 either directly or indirectly via alead extension and header. Alternatively, in some examples, leads 32 maybe implanted and coupled to an external stimulator, e.g., through apercutaneous port. In additional example implementations, stimulator 34may be a leadless stimulator with one or more arrays of electrodesarranged on a housing of the stimulator rather than leads that extendfrom the housing. Application of certain techniques will be described inthis disclosure with respect to implantable stimulator 34 andimplantable leads 32 having ring electrodes for purposes ofillustration. However, other types of electrodes may be used.

Stimulator 34 may be implanted in patient 36 at a location minimallynoticeable to the patient. For SCS, stimulator 34 may be located in thelower abdomen, lower back, or other location to secure the stimulator.Leads 32 are tunneled from stimulator 34 through tissue to reach thetarget tissue adjacent to spinal cord 38 for stimulation delivery. Atthe distal ends of leads 32 are one or more electrodes (not shown) thattransfer the stimulation pulses from the lead to the tissuesubstantially simultaneously with stimulation pulses delivered via ahousing electrode, e.g., electrode 37. Some of the electrodes may beelectrode pads on a paddle lead, circular (i.e., ring) electrodessurrounding the body of leads 32, conformable electrodes, cuffelectrodes, segmented electrodes, or any other type of electrodescapable of forming unipolar, bipolar or multi-polar electrodeconfigurations.

Implantable stimulator 34 delivers stimulation to spinal cord 38 toreduce the amount of pain perceived by patient 36. As mentioned above,however, the stimulator may be used with a variety of differenttherapies, such as peripheral nerve stimulation (PNS), peripheral nervefield stimulation (PNFS), deep brain stimulation (DBS), corticalstimulation (CS), pelvic floor stimulation, peripheral nervestimulation, gastric stimulation, and the like. The stimulationdelivered by implantable stimulator 34 may take the form of stimulationpulses or continuous stimulation waveforms, and may be characterized bycontrolled current or voltage levels, as well as programmed pulse widthsand pulse rates in the case of stimulation current pulses. Stimulationmay be delivered via selected combinations of electrodes located on oneor both of leads 32 and on the housing. Stimulation of spinal cord 38may, for example, prevent pain signals from traveling through the spinalcord and to the brain of the patient. Patient 34 perceives theinterruption of pain signals as a reduction in pain and, therefore,efficacious therapy.

With reference to FIG. 2, a user, such as a clinician or patient 36, mayinteract with a user interface of external programmer 40 to programstimulator 34. Programming of stimulator 34 may refer generally to thegeneration and transfer of commands, programs, or other information tocontrol the operation of the stimulator. For example, programmer 40 maytransmit programs, parameter adjustments, program selections, groupselections, or other information to control the operation of stimulator34, e.g., by wireless telemetry.

In some cases, external programmer 40 may be characterized as aphysician or clinician programmer, such as clinician programmer 20 (FIG.1), if it is primarily intended for use by a physician or clinician. Inother cases, external programmer 40 may be characterized as a patientprogrammer, such as patient programmer 22 (FIG. 1), if it is primarilyintended for use by a patient. In general, a physician or clinicianprogrammer may support selection and generation of programs by aclinician for use by stimulator 34, whereas a patient programmer maysupport adjustment and selection of such programs by a patient duringordinary use.

Whether programmer 40 is configured for clinician or patient use,programmer 40 may communicate to implantable stimulator 4 or any othercomputing device via wireless communication. Programmer 40, for example,may communicate via wireless communication with implantable stimulator 4using radio frequency (RF) telemetry techniques known in the art.Programmer 40 may also communicate with another programmer or computingdevice via a wired or wireless connection using any of a variety oflocal wireless communication techniques, such as RF communicationaccording to the 802.11 or Bluetooth specification sets, infraredcommunication according to the IRDA specification set, or other standardor proprietary telemetry protocols. Programmer 40 may also communicatewith another programming or computing device via exchange of removablemedia, such as magnetic or optical disks, or memory cards or sticks.Further, programmer 40 may communicate with implantable stimulator 4 andother programming devices via remote telemetry techniques known in theart, communicating via a local area network (LAN), wide area network(WAN), public switched telephone network (PSTN), or cellular telephonenetwork, for example.

FIG. 3 is a block diagram illustrating various components of an exampleimplantable stimulator 34. Although the components shown in FIG. 3 aredescribed in reference to implantable stimulator 34, the components mayalso be included within implantable stimulator 4 shown in FIG. 1 andused within system 2. In the example of FIG. 3, implantable stimulator34 includes processor 50, memory 52, power source 54, telemetry module56, antenna 57, and a stimulation generator 60. Implantable stimulator34 is also shown in FIG. 3 coupled to electrodes 48A-Q (collectively“electrodes 48”). Electrodes 48A-48P are implantable and may be deployedon one or more implantable leads. With respect to FIG. 1, lead segments12A and 12B may carry electrodes 48A-H and electrodes 48I-P,respectively. In some cases, one or more additional electrodes may belocated on or within the housing of implantable stimulator 34, e.g., toprovide a common or ground electrode or a housing anode. With respect toFIG. 2, leads 32A and 32B may carry electrodes 48A-H and electrodes48I-P, respectively. In the examples of FIGS. 1 and 2, a lead or leadsegment carries eight electrodes to provide an 2×8 electrodeconfiguration (two leads with 8 electrodes each), providing a total ofsixteen different electrodes. The leads may be detachable from a housingassociated with implantable stimulator 34, or be fixed to such ahousing.

In other examples, different electrode configurations comprising asingle lead, two leads, three leads, or more may be provided. Inaddition, electrode counts on leads may vary and may be the same ordifferent from a lead to lead. Examples of other configurations includeone lead with eight electrodes (1×8), one lead with 12 electrodes(1×12), one lead with 16 electrodes (1×16), two leads with fourelectrodes each (2×4), three leads with four electrodes each (3×4),three leads with eight electrodes each (3×8), three leads with four,eight, and four electrodes, respectively (4-8-4), two leads with 12 or16 electrodes (2×12, 2×16), or other configurations. Differentelectrodes are selected to form electrode combinations. Polarities areassigned to the selected electrodes to form electrode configurations.

Electrode 48Q represents one or more electrodes that may be carried on ahousing, i.e., can, of implantable stimulator 4. Electrode 48Q may beconfigured as a regulated or unregulated electrode for use in anelectrode configuration with selected regulated and/or unregulatedelectrodes among electrodes 48A-48P, which may be located on a lead bodyof one or more leads, as described above. Electrode 48Q may be formedtogether on a housing that carries the electrode and houses thecomponents of implantable stimulator 4, such as stimulation generator60, processor 50, memory 52, telemetry module 56, and power source 54.

In accordance with this disclosure, housing electrode 48Q may beconfigured for use as an anode to source current substantiallysimultaneously with current sourced by another electrode 48A-48Pconfigured for use as an anode. By way of specific example, electrodes48A, 48B, and housing electrode 48Q each could be configured for use asanodes. Electrodes 48A, 48B could deliver electrical stimulation currentsubstantially simultaneously with the electrical stimulation currentdelivered via housing electrode 48Q. In this illustration, one or morecathodes could be formed with other electrodes (e.g., any of electrodes48C-48P) on the leads to sink current sourced by anodes 48A, 48B and48Q.

In further accordance with this disclosure, housing electrode 48Q may beconfigured for use as a cathode to sink current substantiallysimultaneously with current sunk by another electrode 48A-48P configuredfor use as a cathode. By way of specific example, electrodes 48A, 48B,and housing electrode 48Q each could be configured for use as cathodes.Electrodes 48A, 48B could deliver electrical stimulation currentsubstantially simultaneously with the electrical stimulation currentdelivered via housing electrode 48Q. In this illustration, one or moreanodes could be formed with other electrodes (e.g., any of electrodes48C-48P) on the leads to source current sunk by cathodes 48A, 48B and48Q.

As used throughout this disclosure, the phrase “delivering electricalstimulation current” may refer to delivery of a source current by anelectrode that sources current (anode), e.g., from a reference voltagefor an unregulated mode or from a regulated current source for aregulated mode, or to delivery of a sink current by an electrode thatsinks current (cathode), e.g., to a reference voltage for an unregulatedmode or to a regulated current sink for a regulated mode. In otherwords, “delivering” as used in this disclosure is directionless in that“delivering” may refer to current flowing into or out of the electrode.So, an electrode configured as anode may deliver electrical stimulationcurrent having a first polarity, i.e., a positive polarity, and anelectrode configured as a cathode may also deliver electricalstimulation current having a second polarity, i.e., a negative polarity.

Memory 52 may store instructions for execution by processor 50,stimulation therapy data, sensor data, and/or other informationregarding therapy for patient 6. Processor 50 may control stimulationgenerator 60 to deliver stimulation according to a selected one or moreof a plurality of programs or program groups stored in memory 52. Memory52 may include any electronic data storage media, such as random accessmemory (RAM), read-only memory (ROM), electronically-erasableprogrammable ROM (EEPROM), flash memory, or the like. Memory 52 maystore program instructions that, when executed by processor 50, causethe processor to perform various functions ascribed to processor 50 andimplantable stimulator 4 in this disclosure.

Processor 50 may include one or more microprocessors, digital signalprocessors (DSPs), application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), or other digital logiccircuitry. Processor 50 controls operation of implantable stimulator 4,e.g., controls stimulation generator 60 to deliver stimulation therapyaccording to a selected program or group of programs retrieved frommemory 52. For example, processor 50 may control stimulation generator60 to deliver electrical signals, e.g., as stimulation pulses orcontinuous waveforms, with current amplitudes, pulse widths (ifapplicable), and rates specified by one or more stimulation programs.Processor 50 may also control stimulation generator 60 to selectivelydeliver the stimulation via subsets of electrodes 48, also referred toas electrode combinations, and with polarities specified by one or moreprograms.

Upon selection of a particular program group, processor 50 may controlstimulation generator 60 to deliver stimulation according to theprograms in the groups, e.g., simultaneously or on a time-interleavedbasis. A group may include a single program or multiple programs. Asmentioned previously, each program may specify a set of stimulationparameters, such as amplitude, pulse width and pulse rate, ifapplicable. For a continuous waveform, parameters may include amplitudeand frequency. In addition, each program may specify a particularelectrode combination for delivery of stimulation, and an electrodeconfiguration in terms of the polarities and regulated/unregulatedstatus of the electrodes. The electrode combination may specifyparticular electrodes in a single array or multiple arrays, and on asingle lead or among multiple leads. In accordance with this disclosure,the electrode combination includes at least one anode on the housing ofthe IMD, e.g., electrode 48Q, at least one anode on a lead, electrode48A, and at least one cathode on a lead. The lead-borne anode andcathode may be on the same lead or different leads, if more than onelead is provided.

Stimulation generator 60 is electrically coupled to electrodes 48A-P viaconductors of the respective lead, such as lead 12 in FIG. 1 or leads 32in FIG. 2, in implementations in which electrodes 48A-P are carried by,located on, leads. Stimulation generator 60 may be electrically coupledto one or more housing (“can”) electrodes 48Q via an electricalconductor disposed within the housing of implantable stimulator 4(FIG. 1) or implantable stimulator 34 (FIG. 3). A housing electrode 48Qmay be configured as a regulated or unregulated electrode to form anelectrode configuration in conjunction with one or more of electrodes48A-48P located on leads of the IMD. In accordance with this disclosure,housing electrode 48Q may be configured for use as an anode to sourcecurrent substantially simultaneously with one or more electrodes, e.g.,any of electrodes 48A-48P, on one or more leads configured for use asanodes.

Stimulation generator 60 may include stimulation generation circuitry togenerate stimulation pulses or waveforms and circuitry for switchingstimulation across different electrode combinations, e.g., in responseto control by processor 50. Stimulation generator 60 produces anelectrical stimulation signal in accordance with a program based oncontrol signals from processor 50.

For example, stimulation generator 60 may include a charging circuitthat selectively applies energy from power source 54 to a capacitormodule for generation and delivery of a supply voltage for generation ofstimulation signal. In addition to capacitors, the capacitor module mayinclude switches. In this manner, the capacitor module may beconfigurable, e.g., based on signals from processor 50, to store adesired voltage for delivery of stimulation at a voltage or currentamplitude specified by a program. For delivery of stimulation pulses,switches within the capacitor module may control the widths of thepulses based on signals from processor 50.

In accordance with techniques of this disclosure, stimulation generator60 may be configured to deliver stimulation using one or more ofelectrodes 48A-P as stimulation electrodes, e.g., anodes, whilesubstantially simultaneously delivering stimulation using housingelectrode 48Q as a stimulation electrode, e.g., anode. The anodes on thelead(s) and the housing may be used to deliver stimulation inconjunction with one or more cathodes on the lead(s). As oneillustration, an electrode combination selected for delivery ofstimulation current may comprise an anode on the IMD housing, and anodeon a lead, and a cathode on the same lead or a different lead. In otherexamples, the electrode combination may include multiple anodes and/ormultiple cathodes on one or more leads in conjunction with at least oneanode on the IMD housing. In each case, the electrode combination formsan omnipolar arrangement that may combine at least some characteristicsand benefits of unipolar and bipolar/multipolar arrangements.

Telemetry module 56 may include a radio frequency (RF) transceiver topermit bi-directional communication between implantable stimulator 4 andeach of clinician programmer 20 and patient programmer 22. Telemetrymodule 56 may include an antenna 57 that may take on a variety of forms.For example, antenna 57 may be formed by a conductive coil or wireembedded in a housing associated with medical device 4. Alternatively,antenna 57 may be mounted on a circuit board carrying other componentsof implantable stimulator 4 or take the form of a circuit trace on thecircuit board. In this way, telemetry module 56 may permit communicationwith clinician programmer 20 and patient programmer 22 in FIG. 1 orexternal programmer 40 in FIG. 2, to receive, for example, new programsor program groups, or adjustments to programs or program groups.

Power source 54 may be a non-rechargeable primary cell battery or arechargeable battery and may be coupled to power circuitry. However, thedisclosure is not limited to embodiments in which the power source is abattery. In another embodiment, as an example, power source 54 maycomprise a supercapacitor. In some embodiments, power source 54 may berechargeable via induction or ultrasonic energy transmission, andinclude an appropriate circuit for recovering transcutaneously receivedenergy. For example, power source 54 may be coupled to a secondary coiland a rectifier circuit for inductive energy transfer. In additionalembodiments, power source 54 may include a small rechargeable circuitand a power generation circuit to produce the operating power.Recharging may be accomplished through proximal inductive interactionbetween an external charger and an inductive charging coil withinstimulator 4. In some embodiments, power requirements may be smallenough to allow stimulator 4 to utilize patient motion at least in partand implement a kinetic energy-scavenging device to trickle charge arechargeable battery. A voltage regulator may generate one or moreregulated voltages using the battery power.

FIG. 4 is a functional block diagram illustrating various components ofan external programmer 40 for an implantable stimulator 14. Although thecomponents shown in FIG. 4 are described in reference to externalprogrammer 40, the components may also be included within clinicianprogrammer 20 or patient programmer 22 shown in FIG. 1. As shown in FIG.4, external programmer 40 includes processor 53, memory 55, telemetrymodule 57, user interface 59, and power source 61. In general, processor53 controls user interface 59, stores and retrieves data to and frommemory 55, and controls transmission of data with implantable stimulator34 through telemetry module 57. Processor 53 may take the form of one ormore microprocessors, controllers, DSPs, ASICS, FPGAs, or equivalentdiscrete or integrated logic circuitry. The functions attributed toprocessor 53 herein may be embodied as software, firmware, hardware orany combination thereof.

Memory 55 may store instructions that cause processor 53 to providevarious aspects of the functionality ascribed to external programmer 40in this disclosure. Memory 55 may include any fixed or removablemagnetic, optical, or electrical media, such as RAM, ROM, CD-ROM,magnetic disks, EEPROM, or the like. Memory 55 may also include aremovable memory portion that may be used to provide memory updates orincreases in memory capacities. A removable memory may also allowpatient data to be easily transferred to another computing device, or tobe removed before programmer 40 is used to program therapy for anotherpatient. Memory 55 may also store information that controls operation ofimplantable stimulator 4, such as therapy delivery values.

A clinician or patient 36 interacts with user interface 59 in order to,for example, manually select, change or modify programs, adjust voltageor current amplitude, provide efficacy feedback, or view stimulationdata. User interface 59 may include a screen and one or more inputbuttons that allow external programmer 40 to receive input from a user.The screen may be a liquid crystal display (LCD), plasma display, dotmatrix display, or touch screen. The input buttons may include a touchpad, increase and decrease buttons, emergency shut off button, and otherinput media needed to control the stimulation therapy.

Telemetry module 57 allows the transfer of data to and from stimulator34. Telemetry module 57 may communicate automatically with stimulator 34at a scheduled time or when the telemetry module detects the proximityof the stimulator. Alternatively, telemetry module 57 may communicatewith stimulator 34 when signaled by a user through user interface 59. Tosupport RF communication, telemetry module 44 may include appropriateelectronic components, such as amplifiers, filters, mixers, encoders,decoders, and the like.

Programmer 40 may communicate wirelessly with implantable stimulator 34using, for example, RF communication or proximal inductive interaction.This wireless communication is possible through the use of telemetrymodule 44 which may be coupled to an internal antenna or an externalantenna. Telemetry module 44 may be similar to telemetry module 57 ofimplantable stimulator 34.

Programmer 40 may also be configured to communicate with anothercomputing device via wireless communication techniques, or directcommunication through a wired, e.g., network, connection. Examples oflocal wireless communication techniques that may be employed tofacilitate communication between programmer 24 and another computingdevice include RF communication based on the 802.11 or Bluetoothspecification sets, infrared communication, e.g., based on the IrDAstandard.

Power source 46 delivers operating power to the components of programmer40. Power source 46 may be a rechargeable battery, such as a lithium ionor nickel metal hydride battery. Other rechargeable or conventionalbatteries may also be used. In some cases, external programmer 40 may beused when coupled to an alternating current (AC) outlet, i.e., AC linepower, either directly or via an AC/DC adapter. Power source 61 mayinclude circuitry to monitor power remaining within a battery. In thismanner, user interface 59 may provide a current battery level indicatoror low battery level indicator when the battery needs to be replaced orrecharged. In some cases, power source 61 may be capable of estimatingthe remaining time of operation using the current battery.

FIG. 5 is a block diagram illustrating various components of an examplestimulation generator 60A. Stimulation generator 60A may be used with animplantable stimulator, e.g., to perform the functions of stimulationgenerator 60 as described with reference to FIGS. 1-3. Althoughdescribed with respect to implantable stimulator 4, stimulationgenerator 60A may also be used for implantable stimulator 34, or othertypes of stimulators. In the example of FIG. 5, stimulation generator60A is selectively, e.g., based on a signal from processor 50 (FIG. 3),configured to deliver constant current stimulation pulses to patient 6via various electrode combinations. However, the disclosure is notlimited to examples in which regulated current pulses are delivered. Inother examples, stimulation generator 60A may provide continuous,regulated current waveforms, rather than regulated current pulses. Instill other examples, stimulation generator 60A may deliver combinationsof continuous waveforms and pulses, or selectively deliver eithercontinuous waveforms or pulses. Stimulation generator 60A may generateeither constant current-based or constant voltage-based stimulation inthe form of pulses or continuous waveforms.

In the example illustrated in FIG. 5, stimulation generator 60A includesstimulation control module 62, reference voltage source 64, switch array66, and current regulator array 68. Reference voltage source 64 mayprovide operating power to current regulator array 68, and may include aregulated voltage that sets the level of the reference voltage. As shownin FIG. 5, reference voltage source 64 may be coupled to provideoperating power for the current regulator array 68 and provide areference voltage for connection to electrodes 48A-48Q for anunregulated mode of electrode operation. In other examples, however, thevoltage level of the reference voltage and the operating voltage levelprovided to regulated current source array 68 may be different.

Stimulation control module 62 forms a stimulation controller thatcontrols switch array 66 and current regulator array 68 to deliverstimulation via electrodes 48A-48Q. Stimulation control module 62 mayinclude one or more microprocessors, microcontrollers, digital signalprocessors (DSPs), application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), or other integrated or discretelogic circuitry. In operation, stimulation control module 62 may controldelivery of electrical stimulation according to one or more programsthat may specify stimulation parameters such as electrode combination,electrode polarity, stimulation current amplitude, pulse rate, and/orpulse width as well as the percentage of source current distributedamong or contributed by a housing anode and one or more lead anodes onone or more leads, and the percentage of sink current sunk by one ormore cathodes. Programs may be defined by a user via an externalcontroller and downloaded to an implantable stimulator 4 or 34 for useby stimulation control module 62.

Current regulator array 68 includes a plurality of regulated currentsources or sinks. Again, a current regulator may function as either acurrent source or sink, or be selectively configured to operate aseither a source or a sink. For convenience, however, the term “currentregulator” may be used in some instances to refer to either a source orsink. Hence, each of the current regulators in current regulator array68 may operate as a regulated current source that delivers stimulationvia a corresponding one of electrodes 48A-Q or a regulated current sinkthat receives current from a corresponding one of electrodes 48A-Q,where electrodes 48A-48Q may be provided on leads, on a stimulatorhousing, on a leadless stimulator, or in other arrangements. In general,electrodes 48A-48Q may be referred to below as electrodes 48 forconciseness.

Each switch of switch array 66 couples a corresponding one of electrodes48 to either a corresponding bidirectional current regulator of currentregulator array 68 or to reference voltage 64. In some examples,stimulation control module 62 selectively opens and closes switches inswitch array 66 to configure a housing electrode, e.g., electrode 48Q,and one or more of electrodes 48A-48P on one or more leads as regulatedelectrodes by connection to regulated current sources or sinks incurrent regulator array 68. In other examples, stimulation controlmodule 62 may selectively open and close switches in switch array 66 toconfigure either the housing electrode, e.g., electrode 48Q, or anelectrode on the lead as an unregulated electrode by connection toreference voltage 64. In addition, stimulation control module 62 mayselectively control individual regulated current sources or sinks incurrent regulator array 68 to deliver stimulation current pulses to theselected electrodes.

Reference voltage 64 may be a high or low voltage supplied by aregulated power source, depending on whether an electrode is programmedto be an unregulated source (high voltage rail) or unregulated sink (lowvoltage rail). Hence, reference voltage 64 may produce high and lowreference voltages for selective coupling to unregulated, referenceelectrodes as needed given the selected electrode configuration. Aregulated power source may produce one or more regulated voltage levelsfor use as reference voltage 64 and for use as a power rail for currentregulator array 68. Again, although the same reference voltage 64 iscoupled to current regulator array 68 in FIG. 5, different voltagelevels could be used for the reference voltage coupled to switch array66 and the operating voltage level provided to the regulated currentsource array. A regulated power source may generate the regulatedvoltages from voltages provided by a power source 54 (FIG. 3), such as abattery.

Stimulation control module 62 controls the operation of switch array 66to produce electrode configurations defined by different stimulationprograms. In some cases, the switches of switch array 66 may bemetal-oxide-semiconductor field-effect-transistors (MOSFETs) or othercircuit components used for switching electronic signals. The switchesof switch array 66 may be designed to carry an amount of unregulatedcurrent that may be coupled to a corresponding electrode through anunregulated current path associated with reference voltage 64. Aspreviously described, two or more regulated, stimulation electrodes 48may be intentionally programmed to deliver different amounts of currentsuch that the regulated electrodes produce an unbalanced currentdistribution.

To provide individual control of electrodes 48 as either regulatedelectrodes or as unregulated, reference electrodes, stimulation controlmodule 62 controls operation of switch array 66, and current regulatorarray 68. When stimulation is delivered to patient 6, for the example ofcurrent pulses, stimulation control module 62 controls switch array 66to couple selected stimulation electrodes for a desired electrodecombination to respective current regulators of current regulator array68 or to reference voltage 64, as needed. Stimulation control module 62controls the regulated bidirectional current sources of currentregulator array 68 coupled to regulated electrodes to source or sinkspecified amounts of current. For example, stimulation control module 62may control selected current sources or sinks to on a pulse-by-pulsebasis to deliver current pulses to corresponding electrodes.

Stimulation control module 62 also deactivates the regulatedbidirectional current regulators of current regulator array 68 tied toinactive electrodes, i.e., electrodes that are not active as regulatedelectrodes in a given electrode configuration. Each regulatedbidirectional current regulator of current regulator array 68 mayinclude an internal enable switch controlled by stimulation controlmodule 62 that disconnects regulated power source 64 from the currentregulator or otherwise disables the current source when thecorresponding electrode is not used as a regulated electrode to deliverstimulation.

FIG. 6 is a block diagram illustrating an example of various componentsof stimulation generator 60A shown in FIG. 5 in greater detail. Inparticular, FIG. 6 shows current regulator array 68 and switch array 66in greater detail. As shown in FIG. 6, current regulator array 68includes regulated bidirectional current regulators 68A-Q and switcharray 66 includes switches 78A-78Q and 79A-79Q. Each of bidirectionalcurrent regulators 68A-68Q includes a corresponding one of regulatedcurrent sources 72A-72Q that delivers regulated stimulation current tothe corresponding electrode and a corresponding one of regulated currentsinks 74A-74Q that receives regulated stimulation current from thecorresponding electrode. Note that the block diagram illustrated in FIG.6 is intended as a conceptual diagram that shows how stimulationgenerator 60A can be configured to control the operation of electrodes48 in different modes, i.e., an off mode, regulated modes, and anunregulated, reference mode. Thus, for ease of illustration, not allpower and control signals are shown in FIG. 6.

In the example of FIG. 6, switches 78A-78Q may be coupled at one end toa high voltage reference, which may correspond to a high referencevoltage level of reference voltage 64, and to a corresponding one ofelectrodes 48 at the other end. Switches 79A-79Q may be coupled at oneend to a low voltage reference, which may correspond to low referencevoltage level of reference voltage 64, and to a corresponding one ofelectrodes 48 at the other end. High reference voltage (High Vref) andlow reference voltage (Low Vref) represent high and low voltage levelsof reference voltage 64 (FIG. 5) and may be supplied by power source 54.For example, the high reference voltage may correspond to a referencevoltage level and the low reference voltage may correspond to a groundpotential to which the reference voltage level is referenced.

As further shown in FIG. 6, each regulated current source 72A-72Q may becoupled to the high reference voltage or another upper voltage rail,which supports regulator overhead and sources current that is regulatedby the regulated current source. In addition, each regulated currentsink 74A-74Q may be coupled to the low reference voltage or anotherlower voltage rail or ground potential, which supports regulatoroverhead and sinks current that is regulated by the regulated currentsink.

Stimulation control module 62 controls the operation of regulatedcurrent sources 72A-72Q, sinks 74A-74Q, switches 78A-78Q, and switches79A-79Q to configure electrodes 48A-48Q as either inactive (i.e., off),regulated cathodes, regulated anodes, unregulated cathodes orunregulated anodes. For example, stimulation control module 62 maygenerate control signals to individually control regulated currentsources 72A-72Q to deliver specified amounts of regulated current toelectrodes 48A-48Q, respectively, and thereby configure such electrodesas regulated anodes. Similarly, stimulation control module 62 maygenerate control signals to individually control regulated current sinks74A-74Q to receive specified amounts of regulated currents fromelectrodes 48A-48Q, respectively, and thereby configure such electrodesas regulated cathodes. For example, stimulation control module 62 mayenable the current sources or sinks and also specify control voltages orcurrent to be applied to the source or sinks to control the amount ofcurrent that is sourced or sunk via the respective electrodes 48A-48Q.

Using the techniques of this disclosure, at least one electrode on thehousing, e.g., electrode 48Q, and one or more electrodes on one or moreleads, e.g., one or more of electrodes 48A-48P, may be configured asanodes. In this manner, the housing electrode and one or more leadelectrodes may substantially simultaneously deliver current to a patientas anodes. One or more cathodes may be activated on one or more leads toreceive the stimulation energy, e.g., sink the current, produced by theanodes on the can and lead(s). For example, as one illustration,electrode 48A may be an electrode on a lead and be configured as ananode to source current, electrode 48M may also be an electrode on leadand be configured as a cathode to sink current, and electrode 48Q may bean electrode on the housing and be configured as an anode to sourcecurrent.

By way of specific example, stimulation control module 62 may generate acontrol signal to close switch 78A, thereby coupling lead electrode 48Ato regulated current source 72A, thus configuring lead electrode 48A asa regulated anode. Stimulation control module 62 may then generate acontrol signal to close switch 78Q, thereby coupling housing electrode48Q to regulated current source 72Q, thus configuring housing electrode48Q as a regulated anode. Stimulation control module 62 may alsoconfigure lead electrode 48M (not shown in FIG. 6) as a regulatedcathode by generating a control signal to close switch 79M (not shown inFIG. 6), thereby coupling lead electrode 48M to regulated current sink74M. Regulated current sink 74M receives specified amounts of regulatedcurrents from electrodes 48A and 48Q. Once configured in this manner,processor 50 may control stimulation generator 60 to deliver stimulationaccording to a selected one or more of a plurality of programs orprogram groups stored in memory 52 such that stimulation is deliveredsubstantially simultaneously by both lead electrode 48A and housingelectrode 48Q, and received by lead electrode 48M.

It should be noted that additional lead electrodes may also beconfigured as anodes and additional lead electrodes may be configured ascathodes. In one specific example, lead electrodes 48B and 48C may alsobe configured as regulated anodes, and lead electrode 48P may beconfigured as a regulated cathode. In this manner, there may be aplurality of lead electrodes configured as anodes delivering electricalstimulation substantially simultaneously with the electrical stimulationdelivered by a housing electrode configured as an anode, and a pluralityof lead electrodes configured as cathodes receiving the combinedelectrical stimulation from the lead electrodes and the housingelectrode.

In addition, stimulation control module 62 may generate control signalsto control switches 78A-78Q and 79A-79Q to selectively couple electrodes48A-48Q to the high reference voltage or the low reference voltage,respectively. For example, stimulation control module 62 may generatecontrol signals Xah-Xqh to close switches 78A-78Q, respectively, andcouple electrodes 48A-48Q to the high reference voltage. In this manner,one of electrodes 48A-48Q may be selectively configured as unregulated,reference anodes that source current from the high reference voltage.Similarly, stimulation control module 62 may generate control signalsXal-Xql to close switches 79A-79Q, respectively, and couple electrodes48A-48Q to the low reference voltage.

In an example implementation, each current regulator, in the form ofeither regulated current source 72A-72Q or regulated current sink74A-74Q, may be implemented as a plurality of regulated current sourcesand sinks, respectively, operating in parallel to produce a combined,programmable current level sufficient for a desired stimulation therapy.A regulated current source 72A, for example, may be implemented byseveral parallel current sources (x N) having identical or similarstructures. Similarly, a regulated current sink may be implemented byseveral parallel current sinks (x N) having identical or similarstructures. For example, in accordance with this disclosure, regulatedcurrent source 72Q may be implemented by several parallel currentsources (x N) having identical or similar structures in order to producea combined, programmable current level for a desired stimulation therapydelivered via housing electrode 48Q substantially simultaneously withone or more regulated current sources 72A-72P coupled to one or morelead electrodes 48A-48P. In this manner, stimulation therapy may bedelivered by a combination of electrodes including both the housingelectrode 48Q and one or more lead electrodes 48A-48P. It should benoted that in such a configuration, the one or more regulated currentsources 72A-72P may also be implemented by several parallel currentsources (x N) having identical or similar structures in order to producea combined, programmable current level for a desired stimulationtherapy.

Similarly, a regulated current sink 74A may be implemented as Nparallel, regulated current sinks, each sinking a fraction of a totalregulated to be sunk by electrode 48A. By activating a selected numberof the parallel, regulated current sources forming a regulated currentsource 72A, stimulation control module 62 may control an amount ofregulated source current delivered to a given electrode 48A coupled tothe respective current source. Similarly, by activating a selectednumber of parallel, regulated current sink branches forming a regulatedcurrent sink 74A, stimulation control module 62 may control an amount ofregulated sink current delivered from a given electrode 48A coupled tothe respective current sink.

As an example, each current regulator, e.g., regulated source 72A-72Q orregulated sink 74A-74Q, may be implemented by N parallel currentregulator branches. As an example, N may be equal to 64 in someimplementations. In this type of implementation, stimulation controlmodule 62 may specify a reference source current and a reference sinkcurrent, e.g., based on program data specified automatically or by auser via an external programmer. For each electrode, stimulation controlmodule 62 may further specify a percentage of the reference sourcecurrent or reference sink current to be delivered via the electrode,e.g., based on program data. For example, stimulation control module 62may specify that housing electrode 48Q should source 60% of the currentto be delivered as an anode while lead electrodes 48A, 48B substantiallysimultaneously source 15% and 25%, respectively, of the current to bedelivered as anodes. Stimulation control module 62 may also specify thatlead electrode 48D should sink 100% of the current as a cathode.

A control signal may be applied to each parallel current regulatorbranch such that the current levels produced by all N branches will addup to approximately the reference current level. Based on thepercentage, which may be referred to as a gain ratio, stimulationcontrol module 62 may selectively activate or deactivate a number ofparallel current regulator branches for a given electrode sufficient toproduce the specified percentage of the reference current. In thismanner, stimulation control module 62 selectively scales up or scalesdown the number of active, parallel current regulator branches. If thereference current is 20 milliamps (mA), for example, the control signalis selected such that activation of all N parallel current regulatorbranches would produce 20 mA of source current or sink current, asapplicable, for application via an electrode. In this case, the controlsignal may be selected such that each current regulator branch produces1/N^(th) of the reference current.

If the percentage to be delivered by a given electrode, e.g., housingelectrode 48Q, is 50 percent, then stimulation control module 62activates 50 percent of the N parallel current regulator branches or,conversely, deactivates 50 percent of the N parallel current regulatorbranches. In either case, N/2 parallel current regulator branches areactivated, producing a combined current of 50%×20 mA=10 mA to be sourcedby electrode 48Q in this example. Hence, when activated, each currentregulator may source or sink a finite amount of current, determined as afunction of the control signal, such that the fractional currentsflowing in the parallel regulator branches can be summed to produce anoverall regulated current. If the reference current is changed, theapplicable control signal applied to each current regulator branch ischanged. In the example above, a lead electrode 48A-48P sources, aloneor in combination with the remaining lead electrodes 48A-48P, theremaining 50%×20 mA=10 mA of current, substantially simultaneously withthe 10 mA sourced by housing electrode 48Q.

By specifying percentages of source current and sink current forrespective electrodes, stimulation control module 62 can control currentregulators 72A-72Q and 74A-74Q to precisely and selectively control thecurrent level sourced by housing electrode 48Q and the current levelsourced substantially simultaneously by one or more lead electrodes48A-48P. In addition, the current levels sunk by particular electrodes48A-48Q may also be precisely and selectively control. Further,stimulation control module 62 can support effective steering ofstimulation current to create different electrical stimulation fields orpatterns useful in electrical stimulation therapy.

Using regulated current source 72A and electrode 48A as an example, theoutputs of the parallel current source branches forming the regulatedcurrent source are coupled to electrode 48A such that the electrodereceives a sum of the regulated source currents produced by themultiple, parallel current source branches. A similar arrangement can beprovided for current sinks 74A-74Q. Hence, the description of a singlesource or sink and the representation of a single source or sink in FIG.6 are provided for purposes of illustration, and may represent either asingle source or sink or multiple, parallel sources or sinks configuredas described in this disclosure. Likewise, each switch 78A-78Q, 79A-79Qmay be implemented by a single switch, or by multiple, parallel switchesoperating to support a sum of the multiple, fractional currents sourcedor sunk via each parallel switch.

When turned “ON,” each parallel current source or sink branch mayproduce a known amount of current, defined by the reference current andcorresponding control signal, as described above. In this manner, asource or sink may be considered either ON or OFF, and deliver the samefractional amount of current as other sources or sinks whenever it isON. Alternatively, in some embodiments, each parallel current source orsink could be configured to provide different fractional amounts ofcurrent, or deliver variable amounts of current according to a biassignal. Although it is understood that each given source 72A-72Q or sink74A-74Q may include multiple, parallel source branches or sink branches,and that a given switch 78A-78Q or 79A-79Q may include multiple,parallel switches, this disclosure will generally refer to each ofsources 72A-72Q, sinks 74A-74Q, or switches 78A-78Q, 79A-79Q on asingular basis for ease of illustration.

FIG. 7 is a circuit diagram illustrating an example circuit 180 that maybe used to implement stimulation generator 60A as shown in FIG. 5. Inthe example of FIG. 7, transistors 182-198 are configured and arrangedto operate as an adaptable current source. Diodes 199 operate to protecttransistor 184 from high voltages in the event of leakage current fromtransistor 182. For circuit 180 of FIG. 7, the adaptable current sourcemay represent a number of parallel, adaptable current regulator branchesthat are selectively activated to scale up or down to a desired currentlevel as a percentage of a reference current. Circuit 180 shows one ofthese branches. Each regulated current source may include 64 parallelcurrent regulator branches, each providing 1/64^(th) of the referencecurrent level. Additional information regarding, for example, adaptablecurrent sources may be found in U.S. patent application Ser. No.12/579,220, filed Oct. 14, 2009, entitled “Adaptable Current RegulatorFor Delivery Of Current-Based Electrical Stimulation Therapy,” theentire contents of which being incorporated herein by reference.

The inputs to the example circuit 180 are REG_TOP, ATN, V_GATE, I_FDBK,EN_STG1, V_SW_BIAS, nEN_STG1, EN_OUTPUT, CMN_SRC_EN, nCMN_SRC_EN, aswell as AVSS, and nEN_OUTPUT. REG_TOP, ATN, and AVSS are supply inputsthat drive the elements of circuit 180. V_GATE and I_FDBK are controlinputs that drive various components of circuit 180. EN_STG1, nEN_STG1,EN_OUTPUT, nEN_OUTPUT, CMN_SRC_EN, and nCMN_SRC_EN are logic inputs thatare used to control the operation of circuit 180 as a regulator or as aswitch that couples a corresponding electrode to unregulated highreference voltage, e.g., REG_TOP.

Some of these inputs are used to turn circuit 180 off when thecorresponding electrode is not in use. Accordingly, transistors 191-198are used as switches for controlling the mode of operation of circuit180. Transistors 191 and 192 may function as enable switches used toturn master transistors 188, 183, respectively, OFF and ON. Transistors193 and 196 may function as isolation switches to isolate transistors182, 184 from a front end of the circuit. Transistors 197 and 198 mayfunction as reference switches that bias transistors 182, 184,respectively, during unregulated operation. The isolation and referencetransistors may be operated in a coordinated manner to selectivelyoperate the adaptable current source as a regulated current source or asa switch that couples the corresponding electrode to a reference voltagevia an unregulated current path. In particular, isolation transistors193, 196 and reference transistors 197, 198 may function to selectivelytie transistors 182, 184 into the current mirror and activate cascodecircuitry for regulated current delivery, or separate transistors 182,184 from such circuitry for unregulated current delivery from REG_TOP.The output of circuit 180 is SRC_OUT and is applied to a correspondingelectrode.

AVSS may be a controlled low voltage supply that remains substantiallyconstant and may be provided by a regulated power source. ATN may be ahigh voltage supply rail that remains substantially constant and mayprovide a higher voltage potential than REG_TOP or AVSS. V_GATE is ananalog input signal supplied by stimulation control module 62 whencircuit 180 is operating as a current regulator. The V_GATE signal maybe generated as a function of a reference current specified for eachregulated current source.

If all N parallel branches are operating, the V_GATE signal will causethe voltage regulator to produce a combined current level that isapproximately equal to the reference current level. Again, a percentageassigned to each active electrode may be used to scale up or scale downthe number of active parallel, adaptable regulator branches in a givencurrent regulator to produce a desired fractional current level.Stimulation control module 62 may not supply V_GATE to circuit 180 whencircuit 180 is operating as a switch or is not used for deliveringstimulation.

The following description refers to the operation of circuit 180 in anadaptable manner as either a current regulator or a switch.

Control signals EN_STG1, CMN_SRC_EN, nCMN_SRC_EN, nEN_STG1, andnEN_OUTPUT control transistors 192, 196 and 197, 198, 191, and 193,respectively. Or gate 195 applies a control signal to transistor 194based on the levels of EN_OUTPUT and CMN_SRC_EN. These control signalsare applied to the gates of the corresponding transistors to turn thetransistors OFF and ON as described.

When operating as a current regulator, transistors 191, 192, 197, and198 do not conduct, i.e., are not enabled. Transistor 183 acts as amaster that controls the operation of slave transistor 184 bycontrolling V_GATE_SW. Thus, transistors 183 and 184 may be viewed as amaster transistor and a slave transistor, respectively, in a currentmirror arrangement. V_GATE_SW turns transistor 184 ON and OFF to producea regulated current output signal with a desired current levelcontrolled by the level of the V_GATE signal.

Example circuit 180 uses a configuration incorporating a current mirrorand active cascode to operate as a current regulator. Transistors 183and 184 form a current mirror, as mentioned above, and may be selectedto be well matched to each other. Transistors 182 and 185-190 form anactive cascode configuration that that protects transistor 184 from highvoltages at SRC_OUT and monitors I_SUM so that the V_(DS) of transistors183 and 184 are approximately equal over the operational range ofcircuit 180.

In operation, REG_TOP decreases when delivering stimulation, therebycausing the voltage drop over transistors 182 and 184 to decreaseproportionately. Because of this decrease, the V_(DS) of transistor 182decreases, causing transistor 186 to begin to turn OFF. This, in turn,causes the V_(GS) of transistor 185 to increase and turn transistor 185ON more, thereby decreasing the V_(GS) of transistor 187. Consequently,transistor 187 begins to turn OFF, which causes the V_(GS) of transistor182 to increase. That is, transistor 187 replaces voltage on transistor182, VG_CASC, causing its resistive value to decrease, thereby restoringvoltage on drain-to-source voltage (V_(DS)) of transistor 184 so that itmore closely matches the V_(DS) of transistor 183.

Transistors 188-190 set the current for transistors 185-187 based onI_FDBK. I_FDBK is a reference current and may be generated by circuitryat a front end of example circuit 180. In particular, transistors 188and 189 set the current for transistor 185 and transistor 190 sets thecurrent for transistor 187.

Again, in FIG. 7, transistor 182 may represent multiple, e.g.,sixty-four (64), transistors coupled in parallel with each other thateach receive VG_CASC on their respective gates. As an example, theoutput of transistor 182 may be approximately 100 μA, but the overallsource current may be many times that value, as a result of summation ofmultiple, parallel regulated current branches. In addition, transistor182 also may prevent high voltages from being applied to the output.

When circuit 180 switches from operating as a current regulator to aswitch, transistors 191 and 192 are turned ON, and transistors 193 and196 are turned OFF. Transistors 197 and 198 remain turned OFF. Aftertransistors 193 and 196 are turned OFF for a period of time, transistors197 and 198 are turned ON. This creates a non-overlapping clockgenerator which prevents the supply voltage from shorting throughtransistors 191, 193, and 197. Gate 195 controls transistor 194 to beoff during regulated or unregulated modes. When either of the inputs(EN_OUTPUT or CMN_SRC_EN)_to gate 195 is high, the output of gate 195 ishigh, which turns off transistor 194, allowing the input to transistor182 to be either driven low to ground via transistor 197 (causingtransistor 182 to be driving as a switch in the unregulated mode) or toVG_CASC_BIAS via transistor 193 (as in the regulated mode). In someimplementations, the signals EN_OUTPUT applied to gate 195 andnEN_OUTPUT applied to transistor 193 may be skewed in time slightly toimplement a non-overlapping clock generator. In general, the signalnEN_OUTPUT is essentially the inverse of EN_OUTPUT except for the slighttiming skew in some implementations.

In the unregulated mode, transistors 197 and 198 are turned ON to drivetransistors 182 and 184, respectively, into saturation. Accordingly,SRC_OUT is coupled to the high reference voltage REG_TOP throughtransistors 182 and 184 and circuit 180 sources current based on theamount of current required to be delivered by the stimulation electrodegiven load conditions and current distribution at the stimulated tissuesite adjacent the electrode. In this manner, circuit 180 can beconfigured to operate as either an unregulated current path or aregulated current path.

Circuit 180 is turned OFF when the corresponding electrode is inactive,i.e., not used in an electrode configuration for delivering stimulationtherapy. Transistors 191, 192, 193, 194, and 196 are turned ON andtransistors 197 and 198 are turned OFF when circuit 180 is turned OFF.When transistors 191 and 192 are turned ON, the active cascode(transistors 185-190) and transistor 183 are turned OFF.

Transistors 182-198 may be implemented as N-type and P-type MOSFETtransistors configured to operate in a depletion mode. It should beunderstood, however, that circuit 180 may be implemented using varioustypes and configurations of transistors.

FIG. 8 is a circuit diagram illustrating an example circuit 200 that maybe used to implement stimulation generator 60A as shown in FIG. 5.Example circuit 200 depicts an adaptable, regulated current sink. Inputsto circuit 200 are REG_TOP, REG_BTM, V_GATE, FDBK_BIAS, EN_STG1,nEN_STG1, and CMN_SNK_EN, and VG_CASC, as well as BPLUS, nCMN_SNK_EN,and nEN_OUTPUT. REG_TOP, REG_BTM, V_GATE, FDBK_BIAS, and LV_SW_RAIL aresupply inputs that drive elements of circuit 200. EN_STG1, nEN_STG1,CMN_SNK_EN, nCMN_SNK_EN, and nEN_OUTPUT are logic inputs that are usedto control the operation of circuit 200 as a current regulator or as aswitch that couples a corresponding electrode to an unregulated lowreference voltage, e.g., REG_BTM.

The logic inputs are also used to turn circuit 200 OFF when thecorresponding electrode is not in use. Accordingly, transistors 211 and212 may function as enable switches used to turn master transistors 208,203, respectively, OFF and ON. Transistors 213 and 214 may function likeisolation switches to selectively isolate transistors 202, 204 from thefront end of the sink circuit. Transistors 215 and 216 may function asreference switches that bias transistors 202, 204 during unregulatedmode. The isolation transistors 213, 214 and reference transistors 215,216 may be operated in a coordinated manner to selectively operate theadaptable current sink as a regulated current sink or as a switch thatcouples the corresponding electrode to a reference voltage via anunregulated current path. In particular, isolation transistors 213, 214and reference transistors 215, 216 may function to selectively tietransistors 202, 204 into the current mirror and activate cascodecircuitry for regulated current delivery, or separate transistors 203,204 from such circuitry for unregulated current delivery from REG_BTM.The output of circuit 200 is SNK_OUT and is applied to a correspondingelectrode.

REG_TOP and REG_BTM are positive and negative voltages supplied asreference voltages. V_GATE is an analog input signal with desiredstimulation parameters supplied by stimulation control module 62 whencircuit 200 operates as a current regulator. Stimulation control module62 may not supply V_GATE to circuit 200 when circuit 200 is operating asa switch or is not in use. In some examples, REG_BTM need not be anegative voltage and may instead by a ground or other reference voltage.

The following provides a description of the operation of circuit 200 asa current regulator and as a switch. When operating as a currentregulator and, more specifically, as a regulated current sink,transistors 211, 212, 215, and 216 are turned OFF and transistors 213and 214 are turned ON. In this configuration, transistor 203 controlsthe operation of transistor 204 by controlling the gate voltage oftransistor 204, V_GATE_SW. This turns transistor 204 ON and OFF toproduce a regulated current output signal with the desired signalparameters set by input signal V_GATE. Consequently, transistors 203 and204 may be viewed as a master transistor and a slave transistor,respectively.

To operate as a regulated current sink, example circuit 200 uses aconfiguration that includes a current mirror with well matchedtransistors and a plurality of transistors operating as an activecascode configuration. Transistors 203 and 204 may be configured tooperate as a current mirror and selected to be well matched to eachother, and transistors 202 and 205-210 may operate as an active cascodecircuit that protects transistor 204 from high voltages at SINK_OUT andmonitors I_SUM so that the V_(DS) of transistor 203 and the V_(DS) of204 are approximately equal over the operational range of circuit 200.

In operation, REG_TOP decreases when delivering stimulation therebycausing the voltage drop over transistors 202 and 204 to decreaseproportionately due to the decreased headroom of the bilateral circuit.Because of this decrease, the V_(DS) of transistor 202 decreases causingtransistor 207 to begin to turn OFF. This, in turn, causes the V_(GS) oftransistor 205 to increase and turn transistor 205 ON more, therebydecreasing the V_(GS) of transistor 206. Consequently, transistor 206begins to turn OFF, which causes the V_(GS) of transistor 202 toincrease. That is, transistor 206 replaces voltage on transistor 202,VG_CASC, causing its resistive value to decrease, thereby restoringvoltage on V_(DS) of transistor 204.

Transistors 208-210 set the current for transistors 205-207 based onI_FDBK. I_FDBK is a reference current and may be generated by circuitryat the front end of example circuit 200. In particular, transistor 208generates a V_(GS) which is then applied to transistors 209 and 210.This then sets the current for transistor 205 and transistor 206,respectively, therapy causing transistors 209 and 210 to operate ascurrent sources.

When circuit 200 operates as a switch, transistors 211 and 212 areturned ON and transistors 213 and 214 are turned OFF. Transistors 214and 216 may remain OFF for a period of time before being turned ON toprevent the supply voltage from shorting through transistors 216, 214and 212. In this configuration, transistors 215 and 215 drivetransistors 202 and 204 into saturation. This results in SNK_OUT beingcoupled to the low reference voltage REG_BTM through transistors 202 and204 and circuit 200 sinks an amount of current based on the amount ofcurrent required to be sunk by the stimulation electrode given loadconditions and current distribution at the stimulated tissue siteadjacent the electrode. In this manner, circuit 200 can be configured tooperate as either an unregulated current path or a regulated currentpath.

Circuit 200 may be turned OFF by turning ON transistors 211, 212, 214and 217 and turning OFF transistors 213, 215 and 216. Turning ONtransistors 211 and 212 turns OFF the active cascode transistors and themaster transistor, i.e., transistors 205-210, and transistor 203,respectively. Transistor 217 serves to turn transistor 202 OFF when itis need to be in a high impedance state. Transistor 217 ties the gate(VG_CASC) of transistor 202 to ground, effectively turning transistor202 OFF.

Transistors 202-217 may be implemented as N-type and P-type MOSFETtransistors configured to operate in a depletion mode. It should beunderstood, however, that circuit 200 may be implemented using varioustypes and configurations of transistors. Because transistors 213-217 aresmall in size compared to output transistor 202, circuit 200 may besmaller in size than a circuit 130 (FIG. 9) that includes additionalswitches and, therefore, more easily implemented with a reduced chipsize.

As mentioned above, techniques of this disclosure support deliveringelectrical stimulation current via a housing anode of an IMD whilesubstantially simultaneously delivering electrical stimulation currentvia one or more anodes on one or more leads engaged to the IMD.Alternatively, the techniques may comprise delivering electricalstimulation current via a housing cathode of an IMD while substantiallysimultaneously delivering stimulation current via one or more cathodesand one or more anodes on one or more leads engaged to the IMD. Suchconfigurations may allow a user to control current paths between ahousing-based anode and a lead-based anode(s), for example, in arelative manner to achieve different electric field shapes, sizes, orlocations. In some examples in which the housing electrode is configuredas a cathode to deliver stimulation current substantially simultaneouslywith one or more cathodes and one or more anodes on one or more leadsengaged to the IMD, the amplitude of the cathode current may be kept ata subthreshold level. By combining aspects of a bipolar or multipolarstimulation arrangement, e.g., by using anodes on one or more leads tosource current, with aspects of a unipolar stimulation arrangement,e.g., by using an anode on the housing of the IMD, the system mayprovide an omnipolar stimulation arrangement that delivers to a usermore localized stimulation while consuming less power than may beachievable using bipolar or multipolar stimulation.

Referring to FIGS. 6-8, in one specific example, a bipolar or multipolarstimulation arrangement may be combined with a unipolar arrangement byapplying the output of circuit 180, SRC_OUT, from one current source toa lead anode, e.g., lead electrode 48A while substantiallysimultaneously applying SRC_OUT from another current source to thehousing anode, e.g., housing electrode 48Q. The output of circuit 200,SNK_OUT, is applied to a lead cathode, e.g., lead electrode 48B (ormultiple lead cathodes), in order to sink the summed current applied bythe housing electrode and the lead electrode. Additional lead electrodesmay be similarly configured as anodes and cathodes to source or sinkadditional current as needed.

FIGS. 9A and 9B are conceptual diagrams illustrating two differentimplantable stimulation leads. Leads 300 and 302 are embodiments ofleads 12A and 12B shown in FIGS. 1 and 2. As shown in FIG. 9A, lead 300includes four electrodes 304 (includes electrodes 304A-304D) mounted atvarious lengths of lead body 306.

Electrodes 304A, 304B, 304C, and 304D are equally spaced along the axiallength of lead body 306 at different axial positions. Although notdepicted, in some examples, each electrode 304 may have two or moreelectrodes located at different angular positions around thecircumference of lead body 306, forming segmented electrodes. Electrodesof one circumferential location may be lined up on an axis parallel tothe longitudinal axis of lead 300. Alternatively, different electrodesmay be staggered around the circumference of lead body 306. In addition,lead 300 or 302 may include asymmetrical electrode locations around thecircumference of each lead or electrodes of the same level that havedifferent sizes. These electrodes may include semi-circular electrodesthat may or may not be circumferentially aligned. Lead body 306 mayinclude a radiopaque stripe (not shown) along the outside of the leadbody.

FIG. 9B illustrates lead 302 that includes more electrodes than lead300. Lead 302 includes lead body 308. Eight electrodes 310 (310A-310H)are located at the distal end of lead 302. Each electrode 310 may beevenly spaced from one or more adjacent electrode and includes one ormore electrodes. Although not depicted, in some examples, each electrode310 includes four electrodes distributed around the circumference oflead body 308. Therefore, lead 302 may include 32 electrodes in someexample configurations. Each electrode may be substantially rectangularin shape. Alternatively, the individual electrodes may have alternativeshapes, e.g., circular, oval, triangular, or the like.

FIG. 10 is a conceptual diagram illustrating an example paddle lead 320that may be used for delivering electrical stimulation in accordancewith the techniques in this disclosure. In the example of FIG. 10, lead320 includes a lead body 322 and a lead paddle section 324 carrying anarray of electrodes 326 arranged in three rows having five, six and fiveelectrodes, respectively. Electrodes indicated by plus (+) signs areanodes, electrodes indicated by minus (−) signs are cathodes, andelectrodes without signs are inactive electrodes. Paddle lead 320 may beconfigured to include lesser or greater numbers of electrodes. In someimplementations, paddle lead 320 may be similar to the Specify™ 5-6-5paddle lead commercially available from Medtronic, Inc. of Minneapolis,Minn.

FIG. 11 is conceptual diagram illustrating a stimulation field that maybe produced using a bipolar stimulation arrangement. FIG. 11 depictsstimulation field 330 produced using lead 300, as shown in FIG. 9A. Aspreviously mentioned, a bipolar stimulation arrangement, i.e., anarrangement in which any anode delivering current, or cathode receivingcurrent, is located on one or more leads, may provide stimulation fieldsthat are smaller and have localized shapes (due to the close proximitybetween the anodes and cathodes) as compared to the sphere-like fieldcreated by a unipolar stimulation arrangement. In the example shown inFIG. 11, stimulation field 330 is produced when electrode 304B isconfigured to act as an anode and source current, and electrode 304C isconfigured to act as a cathode and sink the current sourced by electrode304B, acting as an anode. Although not depicted in FIG. 11, multipleanodes and/or multiple cathodes on one or more leads may be used tocreate a stimulation field in multipolar stimulation arrangement. Asseen in FIG. 11, a bipolar stimulation arrangement may produce alocalized and tightly constrained stimulation field 330 due to theproximity of the anode and cathode, namely electrodes 304B and 304C,respectively, used to produce field 330. In this manner, a bipolarstimulation arrangement producing such a localized and tightlyconstrained stimulation field may be particularly useful in specificallytargeting one or more stimulation sites of a patient.

FIG. 12 is a conceptual diagram illustrating a unipolar stimulationarrangement. FIG. 12 depicts an electrode on housing 14 of IMD 4 and anelectrode on lead 300. A proximal end of lead 300 is coupled to thehousing of IMD 4, although this is not shown in the example of FIG. 12.In the unipolar stimulation arrangement shown in FIG. 12, an anode onthe housing, e.g., housing electrode 13 or electrode 37 (of FIG. 2),sources current and a cathode, e.g., 304C, on lead 300 sinks current.Although such a configuration may be desirable due to the lower powerconsumption that results from the low impedance path through the tissueof patient 6, the stimulation field produced by a unipolar stimulationarrangement may resemble a large sphere, in contrast to the localizedfield 330 shown in FIG. 11. A large stimulation field may, in somepatients, be less desirable than a smaller stimulation field 330, likein FIG. 11, due to the increased volume of tissue activation that mayresult from a larger field.

In accordance with this disclosure, aspects of a unipolar stimulationarrangement and a bipolar or multipolar stimulation arrangement may becombined, providing an omnipolar stimulation arrangement and therebyallowing a user to control current paths between the can-based anode andthe lead-based anode(s) in a relative manner to achieve differentstimulation field shapes. Such an arrangement may allow a user, e.g.,patient 6, to benefit from the lower power consumption, and thus longerbattery life of IMD 4, that may result from use of a unipolarstimulation arrangement while also benefiting from the smaller, and thusmore localized, stimulation field that may result from the use of abipolar stimulation arrangement. An omnipolar stimulation arrangement asdescribed in this disclosure may also provide programming benefits. Forexample, such an arrangement may require fewer electrode specificationsfrom a user, and may automatically balance stimulation settings toproduce valid settings.

FIGS. 13-16 are conceptual diagrams illustrating exemplaryconfigurations combining bipolar or multipolar stimulation arrangementswith unipolar stimulation arrangements using the techniques of thisdisclosure. In general, FIGS. 13-16 depict a housing anode, e.g.,electrode 13 or electrode 37 (of FIG. 2), sourcing stimulation currentin conjunction with one or more anodes on one or more leads 300substantially simultaneously also sourcing current, as will be describedin more detail below. One or more electrodes on one or more leads areconfigured as cathodes to sink stimulation current. The electrodes onthe housing and on the leads are configured as anodes or cathodes byconfiguring current regulators coupled to the electrodes to source orsink current, respectively. In such a configuration, stimulation currentis delivered to a patient using a combination of a unipolar stimulationarrangement, i.e., a housing electrode configured to act as an anode tosource current, and a bipolar stimulation arrangement, i.e., anelectrode on a lead configured to act as an anode to source current,thereby creating a hybrid stimulation arrangement. For ease ofillustration purposes, lead wires that connect leads to IMD 4 have notbeen shown.

FIG. 13 depicts one example of such a hybrid, omnipolar configuration,in accordance with this disclosure. FIG. 13 depicts an anode on thehousing, e.g., electrode 13 or electrode 37 (of FIG. 2), configured tosource current and a cathode, e.g., 304C, on lead 300 configured to sinkcurrent, thereby producing a first stimulation field (not shown) betweenelectrodes 13, 304C. FIG. 13 further depicts electrode 304B configuredto act as an anode and source current, and electrode 304C configured toact as a cathode and sink the current sourced by electrode 304B, therebyproducing a second stimulation field (not shown) between electrodes304B, 304C. Although FIG. 13 depicts electrode 304C acting as a commoncathode that sinks current sourced by both electrode 13 and electrode304B, it should be noted that a second electrode, e.g., electrodes 304Aor 304D, may be configured to act as a cathode to also sink current. Inother words, the two anodes need not share a common cathode.

In FIG. 13, the size of the stimulation field produced between thehousing anode 13 and the lead anode 304C may be reduced and morelocalized when compared with a stimulation field produced using thearrangement shown in FIG. 12 in which a unipolar stimulation arrangementwas used to provide stimulation. In addition, the configuration shown inFIG. 13 may produce a smaller and more localized stimulation fieldbetween lead electrodes 304B and 304C when compared with theconfiguration shown in FIG. 11 in which a bipolar stimulationarrangement was used to provide stimulation. By combining aspects of abipolar stimulation arrangement, e.g., as shown in FIG. 11, with aspectsof a unipolar stimulation arrangement, e.g., as shown in FIG. 12, thearrangement of FIG. 13 may deliver to a user more localized stimulationwhile consuming less power than would be achievable using bipolarstimulation.

In addition, in accordance with this disclosure, the example stimulationarrangements depicted in FIGS. 13-16 may allow a combination ofelectrodes to be selected to deliver an overall predetermined, summedstimulation current comprising the stimulation current delivered byhousing anode 13 and the one or more lead anodes 304B. As mentionedpreviously, current is delivered substantially simultaneously by ahousing anode and one or more anodes on one or more leads. For example,referring to FIG. 13, first electrode 13, second electrode 304B, andthird electrode 304C may be selected to deliver an overall predeterminedsummed stimulation current comprising the stimulation current deliveredvia first electrode 13 and second electrode 304B. First electrode 13 andsecond electrode 304B may be configured, for example, to each deliver apulse substantially simultaneously. That is, the pulses delivered byfirst electrode 13 and second electrode 304B may overlap one another intime partially or completely. In this manner, the delivered pulses (orwaveforms) may sum together to produce a predetermined combined current.

By way of specific example, patient 6 may desire stimulation therapythat requires a stimulation current of about 50 mA. Patient 6 may firstselect a cathode, e.g., electrode 304C, on lead body 306 to sink acathodal current, e.g., 50 mA, such that adequate therapy coverage isachieved. Housing electrode 13 may be then be recruited as an anode(source) in order to balance the required cathodal current, e.g., 30 mA,thereby taking advantage of the low impedance path through tissue, andthus the low power consumption of such a configuration. Electrode 304Bon lead 300 may also be selected as an anode to deliver, substantiallysimultaneously with the 30 mA delivered by housing electrode 13, theremaining current requirement, i.e., 20 mA, to produce the desiredtherapy, thereby taking advantage of a localized stimulation fieldproduced between the lead electrodes. In such a manner, the exampleimplementation of FIG. 13 may provide a user with flexibility in shapinga stimulation field, minimizing side effects, and fine tuning therapy,while also conserving the power of IMD 4. The example implementation ofFIG. 13 delivers an overall predetermined summed stimulation current,e.g., 50 mA, by delivering current via first electrode 13 (30 mA)substantially simultaneously with current delivered via second electrode304B (20 mA).

In the above example, the specific current levels between the housingelectrode and the lead electrode may be based on a percentage of theoverall current to be delivered, or the actual current amplitudes. Forexample, if the overall current to be delivered is 50 mA, housingelectrode 13 may be selected to deliver 60% of the overall current (30mA) and electrode 304B may be selected to deliver the remaining 40% ofthe overall current (20 mA). Or, rather than use percentages, housingelectrode 13 may be selected to deliver a specific current, e.g., 30 mA,and electrode 304B may be selected to deliver the remaining current,e.g., 20 mA. In another example, the user may select specific values fortwo of three electrodes to be used in delivering stimulation therapy,and the system would then automatically calculate the current to besourced or sunk by the third electrode in order to balance the currents,i.e., overall source current=overall sink current. In one example,housing electrode 13 would be adjusted in order to balance the otherelectrode currents.

As mentioned above, programs generated by a clinician programmer andselected by a user using a patient programmer, for example, specifystimulation parameters. The programs may be defined by the duration,current or voltage source amplitude, current or voltage sink amplitude,pulse width and pulse rate of the stimulation as well as the electrodecombination, the percentage of source current distributed among orcontributed by a housing anode and one or more lead anodes on one ormore leads, and the percentage of sink current sunk by one or morecathodes.

Continuing the example above, a user may select, e.g., using a patientprogrammer, a program that delivers an overall current of 50 mA, withthe housing electrode 13 delivering 60% of the overall current (30 mA)and electrode 304B delivering the remaining 40% of the overall current(20 mA). Processor 50 may retrieve the specific stimulation parametersdefined by the selected program from memory and control stimulationgenerator 60 to deliver stimulation according to the selected program.In particular, stimulation control module 62 of stimulation generator60A, for example, may generate a control signal to close a switch,thereby coupling lead electrode 304B to a regulated current source 72A,thus configuring lead electrode 48A as a regulated anode.

Stimulation control module 62 may then generate a control signal toclose another switch, thereby coupling housing electrode 13 to aregulated current source, thus configuring housing electrode 13 as aregulated anode. Stimulation control module 62 may also configure a leadelectrode, e.g., lead electrode 304C, as a regulated cathode bygenerating a control signal to a close switch, thereby coupling leadelectrode 304C to a regulated current sink. The regulated current sinkreceives specified amounts of regulated currents from anode 13 and 304B.In order for housing electrode 13 to deliver 60% of the overall current,stimulation control module 62 may activate 60 percent of the N parallelcurrent regulators that comprise the current regulator to whichelectrode 13 is coupled. Likewise, in order for lead electrode 304B todeliver 40% of the overall current, stimulation control module 62 mayactivate 40 percent of the N parallel current regulators that comprisethe current regulator to which electrode 304B is coupled.

In addition, the example implementation of FIG. 13 may allow a user tomore effectively shape, focus or steer a stimulation field. Steering astimulation field may allow a user to transition between a unipolarstimulation arrangement and a bipolar (or multipolar) stimulationarrangement or between a bipolar (or multipolar) arrangement and aunipolar arrangement, permitting the user to select different weightedcombinations of current delivered to one or more lead cathodes by thehousing anode and lead anode. The user may stop the transition at adesired point to use both a housing anode and at least one lead anode.This may allow more flexibility in selecting the strength of the anode“shields” on the lead that are in proximity to the cathodes. Further,the example configuration of FIG. 13 may automatically adjust thehousing electrode to balance the currents after a user-requested changeto the contribution of any other electrode. This feature may enhanceusability by relieving the user of having to manually balance currents.

FIG. 14 depicts another example of a stimulation arrangement, inaccordance with this disclosure. The configuration depicted in FIG. 14may produce a first stimulation field using an electrode on IMD 4 and anelectrode on lead 300. In particular, an anode on the housing, e.g.,electrode 13 or electrode 37 (of FIG. 2), sources current and a cathode,e.g., 304B, on lead 300 sinks current, thereby producing a firststimulation field (not shown). A second stimulation field may beproduced when electrode 304A is configured to act as an anode and sourcecurrent, and electrode 304B is configured to act as a cathode and sinkthe current sourced by electrode 304A. Although FIG. 14 depictselectrode 304B acting as a common cathode that sinks current sourced byboth electrode 13 and electrode 304A, it should be noted that a secondelectrode may be configured to act as a cathode to also sink current. Inother words, the two anodes need not share a common cathode.

The configuration shown in FIG. 14 may also produce a third stimulationfield when electrode 304D is configured to act as an anode and sourcecurrent, and electrode 304C is configured to act as a cathode and sinkthe current sourced by electrode 304D. The three stimulation fields addtogether to form one overall field. As in FIG. 13, electrodes may beselected to deliver an overall predetermined summed stimulation currentcomprising the stimulation current delivered via first electrode 13second electrode 304A, and third electrode 304D.

By way of specific example, patient 6 may desire stimulation therapythat requires a stimulation current of 50 mA. Electrodes 304A and 304Don lead 300 may be selected as anodes to deliver, e.g., 30 mA, toproduce the desired therapy, thereby taking advantage of the resultinglocalized stimulation fields (not shown). Can electrode 13 may thendefault to an anode in order to deliver the remaining currentrequirement, e.g., 20 mA, substantially simultaneously with the 30 mAdelivered by electrodes 304A and 304D, for example, thereby takingadvantage of the low impedance path through tissue, and thus the lowpower consumption of such a configuration. In one example, a user mayselect a stimulation program that divides the 20 mA approximatelyequally such that two localized stimulation fields (not shown) are eachproduced by stimulation currents of approximately 10 mA. In such amanner, the example implementation of FIG. 14 may provide a user withflexibility in shaping multiple stimulation fields using a single leadwhile also conserving the power, and thus extending the battery life, ofIMD 4.

FIG. 15 depicts another example of a stimulation arrangement, inaccordance with this disclosure. FIG. 15 is similar to theimplementation shown in FIG. 14, with the addition of a second lead 340having lead body 342 having four electrodes 344 (electrodes 344A-344D)mounted at various lengths of lead body 342. Like FIG. 14, theconfiguration shown in FIG. 15 produces a first stimulation field usinga housing electrode on IMD 4 and an electrode on lead 300. Inparticular, an anode on the housing, e.g., electrode 13, sources currentand a cathode, e.g., 304B, on lead 300 sinks current, thereby producingthe first stimulation field. A second stimulation field is produced whenelectrode 304A is configured to act as an anode and source current, andelectrode 304B is configured to act as a cathode and sink the currentsourced by electrode 304A. A third stimulation field is produced whenelectrode 304D is configured to act as an anode and source current, andelectrode 304C is configured to act as a cathode and sink the currentsourced by electrode 304D.

In the implementation shown in FIG. 15, a fourth stimulation field maybe produced on the second lead, e.g., lead 340. The four fields addtogether to produce one overall stimulation field. The fourthstimulation field may be produced when electrode 344A on lead 340 isconfigured to act as an anode and source current, and electrode 344D onlead 340 is configured to act as a cathode and sink the current sourcedby electrode 344A. The fourth stimulation field may be larger than thesecond and third stimulation fields produced by electrodes on lead 300due to the fact that the currents sourced and sunk by the anode andcathode, electrodes 344A and 344D, respectively, creating the fourthstimulation field are larger than the currents sourced and sunk by theelectrodes used to produce each of second and third stimulation fields.As in FIG. 14, electrodes may be selected to deliver an overallpredetermined summed stimulation current comprising the stimulationcurrent delivered via first electrode 13, second electrode 304A, andthird electrode 304D on lead 300. In addition, second lead 340 may alsoprovide further flexibility in delivering stimulation therapy byallowing additional stimulation field shapes to be used for stimulation.

FIG. 16 depicts another example of a stimulation arrangement, inaccordance with this disclosure. FIG. 16 is similar to theimplementation shown in FIG. 15, depicting IMD 4, first lead 300, andsecond lead 340. As in FIG. 15, the configuration depicted in FIG. 16may produce a first stimulation field using an electrode on IMD 4 and anelectrode on lead 300. In particular, an anode on the housing, e.g.,electrode 13, sources current and a cathode, e.g., 304B, on lead 300sinks current, thereby producing the first stimulation field. A secondstimulation field may be produced when electrode 304A is configured toact as an anode and source current, and electrode 304B is configured toact as a cathode and sink the current sourced by electrode 304A.

Like FIG. 15, the example implementation shown in FIG. 16 includessecond lead 340. In contrast to FIG. 15, however, a third stimulationfield may be created between leads 300, 340. The third stimulation field(not shown) may be produced when electrode 304D on lead 300 isconfigured to act as an anode and source current, and electrode 344C onlead 340 is configured to act as a cathode and sink the current sourcedby electrode 304D. As in FIGS. 13-15, electrodes may be selected todeliver an overall predetermined summed stimulation current.

By way of specific example, patient 6 may desire stimulation therapythat requires a stimulation current of 50 mA. Can electrode 13 may beselected as an anode in order to deliver the majority of the current,e.g., 30 mA, thereby taking advantage of the low impedance path throughtissue, and thus the low power consumption of such a configuration.Electrode 304A on lead 300 may also be selected as an anode to deliver,substantially simultaneously with the 30 mA delivered by can electrode13, the remaining current requirement, e.g., 20 mA, to produce thedesired therapy, thereby taking advantage of the resulting localizedstimulation field (not shown). In such a manner, the exampleimplementation of FIG. 13 may provide a user with flexibility in shapinga stimulation field while also conserving the power of IMD 4. Further,the user may also select a stimulation program that generates thestimulation field (not shown), thereby providing the user withadditional therapeutic effects that may otherwise be unavailable if asingle lead were used.

It should be noted that although leads similar to lead 300 depicted inFIG. 9A were used in the example implementations shown in FIGS. 13-16,leads similar to lead 302 depicted in FIG. 9B may also be used. Inaddition, leads used to implement techniques of this disclosure are notlimited to the leads shown in FIGS. 9A-9B, or the four-electrodeconfigurations depicted in FIGS. 13-16. In some examples, leads mayinclude more or less than four electrodes.

In addition, although not depicted, a paddle lead, e.g., paddle lead 320shown in FIG. 10, may also be used to implement the techniques of thisdisclosure. For example, a paddle lead may replace the single lead 300depicted in FIG. 13. Or, in another example, two paddle leads mayreplace the two leads 300, 340 depicted in FIG. 15. In accordance withthis disclosure, an anode on the can may deliver stimulation currentsubstantially simultaneously with current delivered by an anode on thepaddle lead.

It should also be noted that the techniques of this disclosure are notlimited to implementations that use one or two leads. Rather, any numberof leads may be used. For example, in some implementations, four leadsmay be used. In addition, although the example configurations depictedin FIGS. 13-16 depict can electrode 13 as an anode, as mentioned above,can electrode 13 may also be configured as a cathode. Can cathode 13 maybe used together with one or more cathodes and one or more anodes on oneor more leads in order to deliver stimulation in a manner similar tothat described above.

FIG. 17 is a flow diagram illustrating an example method of deliveringelectrical stimulation using the techniques of this disclosure. In themethod shows in FIG. 17, IMD 4, and in particular, stimulation generator60, delivers electrical stimulation current with a first polarity (i.e.,positive or negative) via a first, or housing/case, electrode of IMD 4carried by housing 14 of IMD 4, e.g., housing electrode 13 or housingelectrode 37 (400). Substantially simultaneously with the electricalstimulation current delivered via the first electrode, IMD 4, and inparticular, stimulation generator 60, delivers electrical stimulationcurrent with the first polarity (i.e., positive or negative) via asecond electrode, e.g., electrode 304B carried by a lead, e.g., lead300, coupled to housing 14 of IMD 4 (410). A third electrode of IMD 4,e.g., electrode 304C, delivers electrical stimulation current with asecond polarity opposite the first polarity (i.e., negative or positive)delivered via the first electrode and the second electrode (420). Thethird electrode may be carried by the lead that includes the secondelectrode, or the third electrode may be carried by another lead. Theelectrical stimulation may be selected to provide at least one of deepbrain stimulation and spinal cord stimulation.

In one example, the first electrode is a first anode, the secondelectrode is a second anode, and the third electrode is a cathode. Inanother example, the stimulation is selected to provide at least one ofdeep brain stimulation and spinal cord stimulation. In yet anotherexample, the first electrode is a first cathode, the second electrode isa second cathode, and the third electrode is an anode.

In one example, using the techniques of this disclosure, the firstelectrode, the second electrode, and the third electrode are selected todeliver an overall predetermined summed stimulation current comprisingthe stimulation current delivered via the first electrode and the secondelectrode.

In some examples, the first electrode is a first anode, and the secondelectrode is one of a plurality of anodes integral with the lead. Inanother example, the lead is a first lead, and the plurality of anodesis a first plurality of anodes. In such an example, IMD 4 may deliverelectrical stimulation current via one of a second plurality of anodesintegral with a second lead substantially simultaneously with theelectrical stimulation current delivered via the first anode and the oneof a second plurality of anodes. In some examples, at least one cathode,e.g., electrode 344C, on the second lead, e.g., lead 340, may receiveelectrical current.

In some examples, stimulation generator 60A may couple the firstelectrode, e.g., electrode 13 or electrode 37, to a first regulatedcurrent path to deliver a first amount of the electrical stimulationcurrent. Stimulation generator 60A may also couple the second electrode,e.g., electrode 304B, via switch array 66, to a second regulated currentpath to deliver a second amount of the electrical stimulation current.Stimulation generator 60A may couple a third electrode, e.g., electrode304C, to a regulated current path to receive a third amount of theelectrical stimulation current approximately equal to a sum of the firstand second amounts of the electrical stimulation current. In oneexample, the first amount of the electrical stimulation current is afirst regulated source current, the second amount of the electricalstimulation current is a second regulated source current, and the thirdamount of the electrical stimulation current is a regulated sink currentthat is approximately equal to a sum of the first and second regulatedsource currents.

As mentioned above, the electrical stimulation may be constantcurrent-based or constant voltage-based stimulation in the form ofpulses or continuous waveforms. In one constant voltage-basedimplementation, the electrical stimulation current delivered by thefirst electrode (anode), i.e., the housing electrode, is a firststimulation current, the electrical stimulation current delivered by thesecond electrode is a second stimulation current, and the electricalstimulation current received by the third electrode is a thirdstimulation current. The first electrode may be coupled to a firstregulated voltage source to deliver the first stimulation current, thesecond electrode may be coupled to a second regulated voltage source todeliver the second stimulation current, and the third electrode may becoupled to a third voltage source to deliver the third stimulationcurrent. In some example constant voltage-based implementations, thethird stimulation current delivered is approximately equal to the sum ofthe first stimulation current and the second stimulation current.

In some example configurations, the case electrode may act as a cathodalcurrent sink. In constant voltage-based implementations of such exampleconfigurations, the first electrode (cathode), i.e., the housingelectrode, may be coupled to a first regulated voltage source to deliver(sink) a first stimulation current, a second electrode may be coupled toa second regulated voltage source to deliver (sink) a second stimulationcurrent, and a third electrode may be coupled to a third voltage sourceto deliver (source) a third stimulation current. In some exampleconstant voltage-based implementations, the third stimulation current isapproximately equal to the sum of the first stimulation current and thesecond stimulation current.

Numerous other configurations are considered to be within the scope ofthis disclosure. Such configurations may include, but are not limited tothe following examples. One example configuration delivers (sources)regulated current via a housing electrode, delivers (sources) regulatedcurrent via a first electrode on a lead, and delivers (sinks) regulatedcurrent via a second electrode on the same or on a different lead.

Another example configuration delivers (sources) regulated current via ahousing electrode, delivers (sources) regulated current via a firstelectrode on a lead, and delivers (sinks), via a second electrode on thesame lead or on a different lead, unregulated current to a referencevoltage. That is, the second electrode is electrically coupled to areference voltage to deliver (sink) unregulated current.

Another example configuration delivers (sources) regulated current via ahousing electrode, delivers (sources) regulated current via a firstelectrode on a lead, and delivers, via a second electrode on the samelead or on a different lead, unregulated current (sources) from areference voltage. That is, the second electrode is electrically coupledto a reference voltage to deliver (source) unregulated current.

Another example configuration delivers (sinks), via a housing electrode,unregulated current, to a reference voltage (i.e., the housing electrodeis electrically coupled to a reference voltage to deliver (sink)unregulated current), delivers regulated current (sources) via a firstelectrode on a lead, and delivers (sources) regulated current via asecond electrode on the same lead or on a different lead.

Another example configuration delivers (sources), via a housingelectrode, unregulated current, from a reference voltage (i.e., thehousing electrode is electrically coupled to a reference voltage todeliver (sources) unregulated current), delivers regulated current(sources) via a first electrode on a lead, and delivers (sinks)regulated current via a second electrode on the same lead or on adifferent lead.

Another example configuration delivers (sinks), via a housing electrode,unregulated current, to a reference voltage (i.e., the housing electrodeis electrically coupled to a reference voltage to deliver (sink)unregulated current), delivers (sources), from a regulated voltagesource, unregulated current via a first electrode on a lead, anddelivers (sinks), to a regulated voltage source, unregulated current viaa second electrode on the same lead or on a different lead.

Another example configuration delivers (sources), via a housingelectrode, unregulated current, from a reference voltage (i.e., thehousing electrode is electrically coupled to a reference voltage todeliver (sources) unregulated current), delivers (sources), from aregulated voltage source, unregulated current via a first electrode on alead, and delivers (sinks), to a regulated voltage source, unregulatedcurrent via a second electrode on the same lead or on a different lead.

FIGS. 18-25 are schematic diagrams illustrating example user interfacespresented by the programmer 40 of FIG. 4. Programmer 40 may representclinician programmer 20 and/or a patient programmer 22 of FIG. 1. FIGS.18-25 generally depict user interfaces that may permit a clinicianand/or patient to transition between a stimulation setting that uses aunipolar electrode arrangement to a stimulation setting that uses abipolar (or multipolar) electrode arrangement, or transition between astimulation setting that uses a bipolar (or multipolar) electrodearrangement to a stimulation setting that uses a unipolar electrodearrangement, and permit a range of hybrid, omnipolar electrodearrangements that make use of various combinations of unipolar andbipolar or multipolar relationships between the electrodes. As will bedescribed in more detail below, FIGS. 18-25 depict two types ofprogramming, electrode-based programming and zone-based programming.

FIG. 18 depicts a user interface illustrating a unipolar stimulationarrangement created using electrode-based programming. FIG. 18 depictsuser interface 59 provided by programmer 40. User interface 59 includesdisplay screen 500. Display screen 500 may be a touchscreen such that astylus, mouse or other pointing device may be used to make selectionsdirectly on screen 500. Alternatively, or in addition, keys, buttons,wheels and other input devices may be provided on programmer 40,independently of display 500. First lead 502 may be added to window 504by first selecting a desired type of lead from pull-down menu 506 andthen selecting “Add Lead 1” via icon 508. Similarly, second lead 510 maybe added to window 504 by selecting the type of lead from pull-down menu512 and then selecting “Add Lead 2” via icon 514. Icons 516, 518 allow auser to remove a lead from window 504. It should be noted that in someexamples, the “Add Lead” icons may not be displayed. The housingelectrode, or “case” electrode, indicated at 520 may, in some examples,be permanently displayed in window 504.

In order to select a unipolar stimulation arrangement, a user may firstuse a stylus to move indicator 522 along horizontal scroll bar 524 untilthe Lead-Case Anode Intensity Balance indicates 1.0, as shown in FIG.18. This indicates that intensity is balanced entirely toward a unipolarstimulation arrangement. Next, in order to create field 526, as in FIG.18, a user may use a stylus, for example, and touch the particularelectrodes 528A-528P depicted on leads 502, 510 that the user seeks tocreate field 526. The user may then use a stylus to move indicator 530along horizontal scroll bar 532 to select the desired electrodeintensity. In FIG. 18, the Selected Electrode Intensity is 0.33, whichis used to weight or scale the electrode contributions by the desiredintensity to get amplitude outputs in stimulation current. The SelectedElectrode Intensity of 0.33 equates in this example to 11.4 mA ofoverall current stimulation, as indicated in current window 533.

Upon selecting the desired electrode intensity, processor 53 ofprogrammer 40 generates field 526 and depicts the currents associatedwith the selected electrodes that are needed to generate field 526.Field 526 may be represented by a line, dashed line, colored region,shaded region, or the like. As shown in FIG. 18, case electrode 520sources the desired 11.4 mA of current while electrode 528C sinks 4.88mA and electrode 528K sinks the remaining 6.51 mA needed to balance thesystem. The currents needed to generate field 526 are shown in window504 as well as in arrays 534, 536, which depict each of the electrodeson each of the two leads and the current in milliamps associated withthe electrodes originally selected by the user. Sliding indicator 530 tothe right increases the electrode intensity, and thus the overallcurrent delivered and field intensity. As such, the currents needed tocreate field 526 will increase. Sliding indicator 530 to the leftdecreases the electrode intensity, and thus the overall currentdelivered and field intensity. As such, the currents needed to createfield 526 will decrease.

In addition, arrays 538, 540 indicate the contributions of theelectrodes originally selected by the user. In the example depicted inFIG. 18, the selected electrode that sinks (or sources, in otherexamples) the most current to produce a given field is assigned a firstcontribution of 1.0, and the contributions of the remaining electrodesused to produce that particular field are scaled in relation to theelectrode having the largest contribution such that the remainingelectrodes are assigned contributions that are a percentage of thatfirst contribution. In FIG. 18, electrode 528K sinks 6.51 mA, a valuegreater than the 4.88 mA sunk by electrode 528C. As such, electrode 528Khas a contribution of 1.0, and electrode 528C has a contribution of 4.88mA/6.51 mA or about 0.75, as indicated in arrays 538, 540. In a unipolararrangement, like in FIG. 18, the case electrode must source all of thedesired current and, as such, it has a contribution of 1.0+0.75=1.75, asindicated at 542.

As mentioned above, in FIG. 18, when the Lead-Case Anode IntensityBalance indicates 1.0, the intensity is balanced entirely toward aunipolar stimulation arrangement. The system then defaults to a unipolarmode, and activates the case to balance the sum of the two electrodesactivated (4.88+6.51=11.40 with a small rounding error). This may beadvantageous because it may require fewer user actions, e.g., the systemautomatically configures case electrode 520, and no user interaction onsubsequent intensity changes, e.g., the user does not have to balancestimulation in order for the system to enter a valid, programmablestate. The system may also default into a more energy efficient modesuch that losses in the lead array are only applied once, because thereturn path does not traverse the lead array wires a second time.

FIG. 19 depicts a user interface illustrating a bipolar/multipolarstimulation arrangement created using electrode-based programming. FIG.19 depicts user interface 59 provided by programmer 40, similar to thatshown in FIG. 18.

In order to select a bipolar/multipolar stimulation arrangement, a usermay first use a stylus to move indicator 522 along horizontal scroll bar524 until the Lead-Case Anode Intensity Balance indicates 0.0, as shownin FIG. 19. This indicates that intensity is balanced entirely toward abipolar/multipolar stimulation arrangement, i.e., case electrode 520will not source any current. Next, in order to create the desired fields526, 544 as in FIG. 19, a user may use a stylus, for example, and touchthe electrodes depicted on leads 502, 510 that the user seeks to createfields 526, 544. The user may then use a stylus to move indicator 530along horizontal scroll bar 532 to select the desired electrodeintensity.

In FIG. 19, the Selected Electrode Intensity is 0.33, which is used toscale the electrode contributions by the desired intensity to getamplitude outputs in stimulation current. The Selected ElectrodeIntensity of 0.33 equates in this example to 11.4 mA of overall currentstimulation, as indicated in current window 533, assuming a maximumcurrent of 35 mA. Upon selecting the desired electrode intensity,processor 53 of programmer 40 generates fields 526, 544 and depicts thecurrents associated with the selected electrodes that are needed togenerate fields 526, 544. As shown in FIG. 19, electrodes 528D and 528L,configured as anodes, source 5.15 mA and 6.25 mA (a total of 11.4 mA),respectively. Electrodes 528C and 528K, configured as cathodes, sink4.88 mA and 6.51 mA (a total of 11.4 mA with a small rounding error),respectively. The currents needed to generate fields 526, 544 are shownin window 504 as well as in arrays 538, 540, which depict each of theelectrodes on each of the two leads and the current in milliampsassociated with the electrodes originally selected by the user. Slidingindicator 530 to the right increases the electrode intensity, and thusthe overall current delivered and field intensity. As such, the currentsneeded to create fields 526, 544 will increase. Sliding indicator 530 tothe left decreases the electrode intensity, and thus the overall currentdelivered and field intensity. As such, the currents needed to createfields 526, 544 will decrease. It should be noted that sliding indicator530 all the way to the left, i.e., lead-case anode intensity balanceequals zero, may require the user to balance the sink and sourcecurrents before a valid combination is achieved.

In addition, arrays 538, 540 indicate the contributions of theelectrodes originally selected by the user. In the example depicted inFIG. 19, the selected electrode that sinks (or sources) the most currentto produce a given field has a first contribution of 1.0, and thecontributions of the remaining electrodes used to produce thatparticular field are a percentage of that first contribution. In FIG.19, electrode 528K sinks 6.51 mA, a value greater than the 4.88 mA sunkby electrode 528C. As such, electrode 528K has a contribution of 1.0,and electrode 528C has a contribution of 4.88 mA/6.51 mA or about 0.75,as indicated in arrays 538, 540. Similarly, electrode 528L sources 6.25mA, a value greater than the 5.15 mA sourced by electrode 528D. As such,electrode 528L has a contribution of 1.0, and electrode 528D has acontribution of 5.15 mA/6.25 mA or about 0.82, as indicated in arrays538, 540. In a multipolar arrangement, like in FIG. 19, the caseelectrode does not source any current. As such, it has a contribution of0.0 mA, as indicated at 542.

FIG. 20 depicts a user interface illustrating a hybrid, or omnipolar,electrode arrangement that makes use of various combinations of unipolarand bipolar relationships between the electrodes, in accordance with thetechniques described above, created using electrode-based programming.FIG. 20 depicts user interface 59 provided by programmer 40, similar tothat shown in FIGS. 18-19.

In order to select an omnipolar stimulation arrangement, a user mayfirst use a stylus to move indicator 522 along horizontal scroll bar 524until the Lead-Case Anode Intensity Balance indicates a value between1.0, or unipolar, and 0.0, or bipolar/multipolar. As shown in FIG. 20,the Lead-Case Anode Intensity Balance indicates a value of 0.43,approximately equally balanced between a unipolar and bipolar/multipolarstimulation arrangement. Next, in order to create the desired fields526, 546 as in FIG. 20, a user may use a stylus, for example, and touchthe electrodes depicted on leads 502, 510 that the user seeks to createfields 526, 546. The user may then use a stylus to move indicator 530along horizontal scroll bar 532 to select the desired electrodeintensity.

In FIG. 20, the Selected Electrode Intensity is 0.33, which is used toscale the electrode contributions by the desired intensity to getamplitude outputs in stimulation current. The Selected ElectrodeIntensity of 0.33 equates in this example to 11.4 mA of overall currentstimulation, as indicated in current window 533. Upon selecting thedesired electrode intensity, processor 53 of programmer 40 generatesfields 526, 546 and depicts the currents associated with the selectedelectrodes that are needed to generate fields 526, 546. As shown in FIG.20, electrodes 528D and 528L, configured as anodes, source 3.25 mA and3.25 mA (a total of 6.5 mA), respectively. Electrodes 528C and 528K,configured as cathodes, sink 4.88 mA and 6.51 mA (a total of 11.4 mAwith a small rounding error), respectively. The remaining current, 4.88mA, is sourced by case electrode 520. The currents needed to generatefields 526, 546 are shown in window 504 as well as in arrays 534, 536,which depict each of the electrodes on each of the two leads and thecurrent in milliamps associated with the electrodes originally selectedby the user.

In addition, arrays 538, 540 indicate the contributions of theelectrodes originally selected by the user. In the example depicted inFIG. 20, the selected electrode that sinks (or sources) the most currentto produce a given field has a first contribution of 1.0, and thecontributions of the remaining electrodes used to produce thatparticular field are a percentage of that first contribution. In FIG.20, electrode 528K sinks 6.51 mA, a value greater than the 4.88 mA sunkby electrode 528C. As such, electrode 528K has a contribution of 1.0,and electrode 528C has a contribution of 4.88 mA/6.51 mA or about 0.75,as indicated in arrays 538, 540. Similarly, electrode 528D sources 3.25mA, a value equal to the 3.25 mA sourced by electrode 528L. As such,electrodes 528D, 528L each have a contribution of 1.0, as indicated inarrays 538, 540. The current sourced by case electrode 520 is comparedto the contributions by the other anodes. As seen in FIG. 20, caseelectrode has a contribution of 4.88 mA/3.25 mA, or 1.50, as indicatedat 542.

The programming techniques discussed above with respect to FIGS. 18-20may provide a convenient and efficient mechanism to balance differentomnipolar current distributions and electrode combinations and evaluatethe results. The techniques may allow a user to transition between astimulation setting that uses a unipolar electrode arrangement to astimulation setting that uses a bipolar electrode arrangement, andpermit a range of hybrid electrode arrangements that make use of variouscombinations of unipolar and bipolar relationships between theelectrodes.

FIG. 21 depicts a user interface illustrating another hybrid, oromnipolar, electrode arrangement that makes use of various combinationsof unipolar and bipolar relationships between the electrodes, inaccordance with the techniques described above, created usingelectrode-based programming. FIG. 21 depicts user interface 59 providedby programmer 40, similar to that shown in FIGS. 18-20.

As shown in FIG. 21, the Lead-Case Anode Intensity Balance indicates avalue of 0.71, indicating that the balance of the stimulationarrangement has been shifted toward a unipolar stimulation arrangement.As before, in order to create the desired fields 548, 551 as in FIG. 21,a user may use a stylus, for example, and touch the electrodes depictedon leads 502, 510 that the user seeks to create fields 548, 551. Theuser may then use a stylus to move indicator 530 along horizontal scrollbar 532 to select the desired electrode intensity. In FIG. 21, theSelected Electrode Intensity has been increased to 0.45, which is usedto scale the electrode contributions by the desired intensity to getamplitude outputs in stimulation current. The Selected ElectrodeIntensity of 0.45 equates in this example to 15.75 mA of overall currentstimulation, as indicated in current window 533. Upon selecting thedesired electrode intensity, processor 53 of programmer 40 generatesfields 548, 551 and depicts the currents associated with the selectedelectrodes that are needed to generate fields 548, 551. As shown in FIG.21, electrodes 528D and 528L, configured as anodes, source 6.75 mA and4.50 mA (a total of 11.25 mA), respectively. Electrodes 528K and 528C,configured as cathodes, sink 9.00 mA and 6.75 mA (a total of 15.75 mA),respectively. The remaining current, 4.50 mA, is sourced by caseelectrode 520. The currents needed to generate fields 548, 551 are shownin window 504 as well as in arrays 534, 536, which depict each of theelectrodes on each of the two leads and the current in milliampsassociated with the electrodes originally selected by the user.

In addition, arrays 538, 540 indicate the contributions of theelectrodes originally selected by the user. In FIG. 21, electrode 528Ksinks 9.00 mA, a value greater than the 6.75 mA sunk by electrode 528C.As such, electrode 528K has a contribution of 1.0, and electrode 528Chas a contribution of 6.75 mA/9.00 mA or about 0.75, as indicated inarrays 538, 540. Similarly, electrode 528D sources 6.75 mA, a valuegreater than the 4.50 mA sourced by electrode 528L. As such, electrode528D has a contribution of 1.0, and electrode 528L has a contribution of4.50 mA/6.75 mA or about 0.67, as indicated in arrays 538, 540. Thecurrent sourced by case electrode 520 is compared to the contributionsby the other anodes. As seen in FIG. 21, case electrode delivers thesame amount of current as electrode 528L and, as such, has acontribution of 0.67, as indicated at 542.

FIG. 22 depicts a user interface illustrating a unipolar stimulationarrangement created using zone-based programming, in contrast to theelectrode-based programming shown in FIGS. 18-21. In zone-basedprogramming, a user may graphically define a desired stimulationfield(s) within zones on or adjacent to one or more leads, and processor53 of programmer 40 may generate the current stimulation required tocreate the stimulation field.

FIG. 22 depicts user interface 59 provided by programmer 40, similar tothat shown in FIGS. 18-21. User interface 59 includes stimulation icon550, shield icon 552, and removal icon 554 that may be used to create adesired stimulation field(s), as will be described in more detail below.User interface 59 includes display screen 500. Display screen 500 may bea touchscreen such that a stylus or other pointing media may be used tomake selections directly on screen 500. Alternatively, or in addition,keys, buttons, wheels and other input devices may be provided onprogrammer 40, independently of display 500.

As described previously, first lead 502 may be added to window 504 byfirst selecting a desired type of lead from pull-down menu 506 and thenselecting “Add Lead 1” via icon 508. Similarly, second lead 510 may beadded to window 504 by selecting the type of lead from pull-down menu512 and then selecting “Add Lead 2” via icon 514. Leads may be added towindow 504 by using a stylus, for example, and touching a location inthe window for placement of the leads. In addition, the user may dragthe leads placed in window 504 to a desired location. Icons 516, 518allow a user to remove a lead from window 504. The housing electrode, or“case” electrode, indicated at 520 may, in some examples, be permanentlydisplayed in window 504.

In order to create field 560, as in FIG. 22, a user may use a stylus,for example, and touch stimulation (“Stim”) icon 550. The user may thenuse the stylus and touch a location, or zone, within window 504. Forexample, the user may touch an electrode on one of leads 502, 510, or alocation near one of the electrodes or leads, e.g., between electrodesand leads. Touching an electrode with the stylus places a stimulationfield on the selected zone, e.g., the lead at the electrode. Touching anarea or zone between a lead or electrode places a stimulation field onthe selected zone, i.e., between the lead or electrode. Individualelectrode values may be determined by their relative proximity to thelocation of the placed field such that the nearest electrode is a fullcontributor (1.0) and others are scaled proportionally. The user mayshape, move, shrink, and expand the stimulation field by dragging, forexample, the stimulation field via the stylus to other areas, or zones,in window 504, e.g., electrodes or areas adjacent to electrodes, inorder to create the desired shape of stimulation field 560. Touchingremoval icon 554 with a stylus will remove the stimulation field.

After a zone has been placed on the display screen, programmer 40 and inparticular processor 53 recruits a set of electrodes, e.g., up to fourelectrodes, to generate the zone. In some examples, one or moreelectrodes may be recruited based on their relative distance from theplaced zone such that their contributions are greater than a minimumthreshold. The electrodes recruited by a zone may have independentcontributions to the shape of the zone between 0 and 1.0, dependent onthe relative distance from the electrode to the zone center. Electrodecontributions may be scaled on a per zone basis such that the highestcontributing electrode(s) are 1.0 and all others are less than or equalto 1.0.

In some examples the scaling of electrodes may be accomplished byfinding the distance between the selected zone placement point and allelectrode centers of leads in the lead placement region. The fourshortest distances that do not cause a lead to be crossed are thenselected for recruitment. Contributions are determined by finding thedistance from the point to the recruited electrodes as a ratio of thetotal distance between electrodes separately in the x and y dimensions.

FIG. 23 is a schematic illustrating an example electrode contributiondetermination. In FIG. 23, the contributions of electrodes E3 and E4 onlead 1 (the left lead) and electrodes E5 and E6 on lead 2 (the rightlead) are determined by finding the distance from the selected zoneplacement point, shown at 561, as a ratio of the total distance betweenthe centers of the electrodes, separately in the x and y dimensions. Thecenters of electrodes E3, E4, E5, and E6 are shown in FIG. 23 at E3_(C), E4 _(C), E5 _(C), and E6 _(C), For lead 1 (the left lead), theelectrode contributions are determined as follows:E3=(X ₁ /X _(tot))*(Y _(0b)/(Y _(0tot))E4=(X ₁ /X _(tot))*(Y _(0a)/(Y _(0tot))And, for lead 2 (the right lead), the electrode contributions aredetermined as follows:E5=(X ₀ /X _(tot))*(Y _(1b) /Y _(1tot))E6=(X ₀ /X _(tot))*(Y _(1a) /Y _(1tot))

The user may then use a stylus to move indicator 562 along horizontalscroll bar 564 to select the desired electrode intensity. Referringagain to FIG. 22, the Selected Zone Intensity is 0.33, which is used toscale the electrode contributions of electrodes automatically selectedto create stimulation field 560 by the desired intensity to generatestimulation current amplitudes. Moving indicator 562 may modify all ofthe electrodes associated with a placed field or zone together. Inaddition, the intensity of the stimulation field is graphically depictedat 566. The Selected Zone Intensity of 0.33 equates in this example to11.4 mA of overall current stimulation, as indicated in current window533. As indicator 562 of horizontal scroll bar 564 is moved to theright, the intensity is increased, depicted graphically at 566 and asindicator 562 of horizontal scroll bar 564 is moved to the left, theintensity is decreased. In some examples, the intensity of caseelectrode 520 may be automatically set in order to balance the othercurrents. In other examples, the user may explicitly set the intensityof case electrode 520. In one example, case electrode 520 may beautomatically configured as an anode, and the user may explicitlyincrease or decrease its intensity using horizontal scroll bar 564 inthe manner described above. The intensity of case electrode 520 isgraphically illustrated at 568. Upon selecting the desired electrodeintensity, processor 53 of programmer 40 generates and depicts thecurrent amplitudes associated with the desired field 560, as seen inwindow 504. In another example, the user may specify whether caseelectrode 520 is an anode or cathode by selecting either the shield orsink icon, respectively, dragging the field, and then setting theintensity via horizontal scroll bar 564.

A user may shape the stimulation field by dragging, for example, thestimulation field boundaries via the stylus to other areas in window504. For example, the user may click on a border, i.e., an outerperimeter, or an area near the border, of the stimulation field, anddrag it inward or outward to resize the stimulation field. When a userclicks on the stimulation field border and drags it, the stimulationfield may, for example, expand in the direction in which the user dragsthe stimulation field.

In addition to shaping the stimulation field by dragging, for example,the stimulation field boundaries via the stylus to other areas in window504, the center of stimulation field 560 may be moved by dragging, forexample, icon 570 representing the intensity of the stimulation field.Dragging center icon 570 of stimulation field 560 may result in theentire stimulation field moving in the direction in which the user dragsthe stimulation field. Dragging the stimulation field may result inadjustments to the currents sunk (or sourced) by the electrodesproducing stimulation 560.

Unlike the examples shown in FIGS. 18-21, zone-based programmingdisplays may not include a horizontal scroll bar for controllingLead-Case Anode Intensity Balance. Rather, the system automaticallydetermines the contributions of the three electrodes on the lead, 0.56,0.75, and 1.00, shown in arrays 572, 574, which depict each of the zoneson each of the two leads. Individual electrode values may be determinedby their relative proximity to the location of the placed field suchthat the nearest electrode is a full contributor (1.0) and others arescaled proportionally. The system then scales the contributions by thedesired intensity to generate stimulation current amplitudes. The systemthen defaults to a unipolar mode, and activates case electrode 520 tobalance the sum of the three electrodes activated (4.92 mA+3.68 mA+2.76mA=11.35 mA, with a small rounding error). This may be advantageousbecause it may require fewer user actions, e.g., the systemautomatically configures the case electrode, and may eliminate the needfor user interactions on subsequent intensity changes, e.g., the userdoes not have to balance stimulation in order for the system to enter avalid, programmable state. The system may also default to the mostenergy efficient mode such that losses in the lead array are onlyapplied once, because the return path does not traverse the lead arraywires a second time.

As shown in FIG. 22, case electrode 520 sources the desired 11.4 mA ofcurrent while electrodes 528I, 528B, 528J sink 2.76 mA, 3.68 mA, and4.92 mA, respectively. The currents needed to generate field 560 areshown in window 504 as well as in arrays 534, 536, which depict each ofthe electrodes on each of the two leads and the current in milliampsassociated with the electrodes within the zones originally selected bythe user. In addition, arrays 572, 574 indicate the contributions of theelectrodes in the zone(s) originally selected by the user. In theexample depicted in FIG. 22, the electrode that sinks (or sources, inother examples) the most current to produce a given field has a firstcontribution of 1.0, and the contributions of the remaining zones usedto produce that particular field are a percentage of that firstcontribution. In FIG. 22, electrode 528J sinks 4.92 mA, a value greaterthan the currents sunk by electrodes 528B, 528I. As such, electrode 528Jhas a contribution of 1.0, and electrodes 528B, 528I have a contributionof 3.68 mA/4.92 mA or about 0.75 and 2.76 mA/4.92 mA, respectively, asindicated in arrays 572, 574. In a unipolar arrangement, like in FIG.22, case electrode 568 must source all of the desired current and, assuch, it has a contribution of 1.0+0.75+0.56=2.31, as indicated at 542.

FIG. 24 depicts a user interface illustrating another unipolarstimulation arrangement created using zone-based programming. FIG. 24 issimilar to the user interface described above with respect to FIG. 22.In FIG. 24, however, indicator 562 of horizontal scroll bar 564 has beenmoved all the way to the right, thereby maximizing electrode intensityat 1.0 for a selected electrode, creating stimulation field 576. In FIG.24, case electrode has been selected to operate at maximum intensity.Maximum intensity may be indicated, for example, by a text message. InFIG. 24, the text message states “An electrode is at max output.” Inother words, one of the electrodes (here, case electrode 520) isstimulating at, or near, its maximum of 35 mA. The intensity of caseelectrode 520 is graphically illustrated at 568. The increased intensityof stimulation field 576 is shown graphically at 566.

In this condition, or in a condition where the user desires to place ananode on the lead array to affect the stimulation field or to guard aphysiological structure such as a dorsal root by causing its neurons tobe hyperpolarized, for example, an anodal ‘shield’ zone can be placed onthe lead array, as will be described in more detail with respect to FIG.25. For example, a user may use a stylus, for example, and touch shield(“Shield”) icon 552. The user may touch an electrode on one of leads502, 510. Touching an electrode with the stylus places an anodal shieldzone on the lead at the electrode. The anodal shield zone may then beshaped by dragging, for example, the shield zone via the stylus to otherareas in window 504, e.g., electrodes, in order to create the desiredshape. Similar to the stimulation field, the intensity of the anodalshield zone may be increased or decreased by selecting the electrode orelectrode combination and moving indicator 562 along horizontal scrollbar 564 to select the desired electrode intensity. As the anodal shieldzone is increased in intensity, for example, the system can continue toautomatically balance the stimulation by preferentially modifying caseelectrode 520 to balance the more therapeutic lead electrodes such thatnet output current is zero, i.e., current sourced by anodes equalscurrent sunk by cathodes, as seen in FIG. 25. Thus, after receiving userinput specifying an adjustment to at least one electrode (e.g., dragginga stimulation field and/or anodal shield zone), the system mayautomatically determine for each electrode not adjusted by the userinput, an amount of electrical stimulation current such that the sum ofthe electrical stimulation currents to be supplied by each of the first,second, and third electrodes equals zero. Then, the system may define anew program to control delivery of the electrical stimulation by thestimulator based on the automatically determined amounts of electricalstimulation currents. In this manner, the system may automaticallybalance, or re-balance, electrical stimulation currents after a usermakes changes to a stimulation field and/or an anodal shield zone.

FIG. 25 depicts a user interface illustrating a hybrid, or omnipolar,electrode arrangement that makes use of various combinations of unipolarand bipolar relationships between the electrodes, in accordance with thetechniques described above, created using zone-based programming. InFIG. 25, the system is operating in a dual mode fashion, such thatstimulation is partially unipolar and partially bipolar/multipolar innature. FIG. 25 depicts the original stimulation field 576 shown in FIG.24. In addition, anodal shield zone 578 is depicted in FIG. 25 with thecurrents associated with the electrodes required to create shield zone578. By moving indicator 562 along horizontal scroll bar 564 to increasethe desired electrode intensity of the electrodes used to create shieldzone 578, the currents associated with the electrodes required to createshield zone 578 also increase.

As mentioned above, as anodal shield zone 578 increases in intensity,the system can continue to automatically rebalance the stimulation suchthat net output current is zero by decreasing the amount of currentsourced by case electrode 520. For example, in FIG. 24, the stimulationzone currents of 8.47 mA, 11.30 mA, and 15.13 mA were balanced by caseelectrode current of 34.90 mA. In FIG. 25, the addition of anodal shieldzone 578 and its associated currents of 9.87 mA and 14.58 mA fromelectrodes 528C and 528K, respectively, require a corresponding drop inthe current sourced by case electrode 520 in order to maintain thesystem balance. In particular, case electrode 250 decreases by 9.87mA+15.58 mA=24.45 mA to 10.45 mA. In this manner, the system transitionsfrom operating in a unipolar stimulation arrangement, as in FIG. 24, tooperating in a dual mode fashion such that stimulation is partiallyunipolar and partially bipolar/multipolar in nature. That is, current issourced by anodes on the lead substantially simultaneously with currentsourced by the case electrode.

FIG. 26 depicts a user interface illustrating a bipolar/multipolarstimulation arrangement created using zone-based programming. Inparticular, as the intensity of anodal shield zone 578 is increased, theutilization of case electrode 520 decreases until it is eventuallyturned off, as shown in FIG. 26. In FIG. 26, a current of 0.06 mA((14.06 mA+20.78 mA)−(8.47 mA+11.30 mA+15.13 mA)) sourced by caseelectrode is insignificant and, as such, may be turned off to maintainefficiency. The system is now operating in a fully bipolar/multipolarmode. The user may receive an indication that the system hastransitioned to a bipolar/multipolar via text message. For example, FIG.26 displays a text message indicating that “Anodes match cathodes.”

Thus, in the manner shown in FIGS. 18-26, the techniques of thisdisclosure allow a user to transition between a stimulation setting thatuses a unipolar electrode arrangement to a stimulation setting that usesa bipolar electrode arrangement, and permit a range of hybrid electrodearrangements that make use of various combinations of unipolar andbipolar relationships between the electrodes.

It should be noted that, in some examples, it may be possible tocontinue increasing the anodal shield zone such that case electrode 520is driven into a cathodal stimulation mode. That is, although the caseelectrode, in general, acts as an additional anodal current source inthe examples described above, in some examples, the case electrode mayact as a cathodal current sink, provided that stimulation at the caseremains at a subthreshold or otherwise innocuous level. Such aconfiguration may result in a small, focused area of stimulation on thelead(s) surrounded by strong anodal shields. In addition, it should benoted that each time the intensity, zone, field, or any other parameteris adjusted via the programmer, these adjustments may be applied to thepatient by downloading the necessary programs, commands, and/oradjustments to the implantable stimulator, e.g., implantable stimulator34, by wireless telemetry. The results of the adjustments may then beevaluated, e.g., to determine efficacy.

The programming techniques discussed above with respect to FIGS. 22-26may provide a convenient and efficient mechanism to balance differentomnipolar current distributions and electrode combinations and evaluatethe results. The techniques may allow a user to transition between astimulation setting that uses a unipolar electrode arrangement to astimulation setting that uses a bipolar electrode arrangement, andpermit a range of hybrid electrode arrangements that make use of variouscombinations of unipolar and bipolar relationships between theelectrodes.

It should be noted that an omnipolar stimulation arrangement may deliveromnipolar electrical stimulation over an entire pulse or over only aportion of a pulse. For example, the first half of a pulse may deliverelectrical stimulation using an omnipolar stimulation arrangement andthe second half of the pulse may deliver electrical stimulation using abipolar/multipolar arrangement. By way of specific example, assume a 200microsecond pulse may be divided into a first half of 100 microsecondsand a second half of 100 microseconds. During the first half of thepulse, i.e., the first 100 microseconds, the housing electrode maysource, i.e., as an anode, 4 mA, a first electrode on a lead may source1 mA, a second electrode on a lead may sink 6 mA, and a third electrodeon a lead may source 1 mA. The first, second, and third electrodes maybe on the same lead or multiple leads. Then, during the second half ofthe pulse, i.e., the second 100 microseconds, the housing electrode maybe turned off, the first electrode may source, i.e., as an anode, 3 mA,the second electrode may sink 6 mA, and the third electrode may source 3mA. In this manner, only a portion of a pulse is delivered via anomnipolar stimulation arrangement.

FIG. 27 is a flow diagram illustrating example operation of theprogrammer for generating a program to control delivery of electricalstimulation. In FIG. 27, a programmer, e.g., external programmer 40,receives, via user interface 59, user input specifying an electrodecombination for delivery of electrical stimulation from an electricalstimulator to a patient. The electrode combination comprises at least afirst electrode carried by a housing of the electrical stimulator, e.g.,case electrode 520, and a second electrode and a third electrode carriedby at least one implantable lead, e.g., leads 502, 510, a coupled to thehousing (600). The second electrode and the third electrode may becarried by the same lead, or by two different leads. For example,electrodes 528A and 528B may form the second and third electrodes,respectively, or electrodes 528A and 528I may form the second and thirdelectrodes, respectively. In some examples, the first electrode is ananode, the second electrode is an anode, and the third electrode is acathode. In other examples, the first electrode is a cathode, the secondelectrode is a cathode, and the third electrode is an anode. In someexamples, specifying an electrode combination comprises using a pointingmedia to select electrodes of the electrode combination. In otherexamples, specifying an electrode combination comprises drags astimulation field relative to the one or more leads. The user mayadditionally add and drag a shield zone relative to the at least onelead.

Additionally, a programmer, e.g., external programmer 40, may receive,via user interface 59, user input specifying amounts of electricalstimulation current to be supplied via the first electrode, the secondelectrode, and the third electrode. For example, a user may select anelectrode and then slide indicator 530 along horizontal scroll bar 532in order to specify the amounts of current to be supplied by each one ofthe first, second, and third electrodes (605). For example, specifyingthe amounts of current may comprise specifying a balance of currentbetween the first electrode, the second electrode, and the thirdelectrode. Specifying the amounts of current may include applyingcurrent levels explicitly, e.g., entering numeric values, using a sliderbar, e.g., a vertical or horizontal scroll bar, by resizing or reshapinga zone, or by other means. The balance of current may comprise anindication of weights assigned to the first electrode, the secondelectrode, and the third electrode. In some examples, the weights areassigned to the first electrode, the second electrode, and the thirdelectrode by adjusting a slidable medium within a range, for exampleindicator 530 of horizontal scroll bar 532.

Finally, the programmer, and in particular processor 53, may define aprogram to control delivery of the electrical stimulation by thestimulator based on the user input received via user interface 59 (610).The program may include the electrode combinations specified as well asstimulation parameters such as duration, current or voltage amplitude,pulse width and pulse rate. The programmer may then download the programto the stimulator to deliver stimulation.

FIG. 28 is a flow diagram illustrating another example operation of theprogrammer for generating a program to control delivery of electricalstimulation. FIG. 28 depicts an example in which stimulation isautomatically balanced after a user adjusts one or more aspects ofstimulation, e.g., a change in one or more electrode contributions, achange in the intensity of one or more aspects of a field, or otherchanges that would result in unbalanced stimulation. A programmer, e.g.,external programmer 40, may receive a request from a user via userinterface 59 to adjust a stimulation field (650). In response, theprogrammer, and in particular processor 53, calculates the caseelectrode contribution necessary to balance the change caused by therequested adjustment (655). Processor 53 may, for example, compare thecalculated case contribution with a case contribution threshold value inorder to determine if the case contribution calculated is achievable(660). If the calculated case contribution is not achievable, e.g., thecalculated case contribution exceeds the threshold value (“NO” at block660), the user is notified, e.g., via user interface 59, that therequested adjustment is not possible (665). If the calculated casecontribution is achievable, e.g., the calculated case contribution doesnot exceed the threshold value (“YES” at block 660), then the programmerprograms the new balanced therapy to the device. The adjustmentrequested by the user may result, for example, in case electrode 520sourcing more or less current, changing from an anode (source) to acathode (sink), or turning off, e.g., if the current sourced or sunk bythe case electrode after the user adjustment is approximately zero orotherwise insignificant.

FIG. 29 is a flow diagram illustrating example operation of theprogrammer for transitioning from a unipolar stimulation arrangement toa hybrid stimulation arrangement, and finally to a bipolar or multipolarstimulation arrangement. Using user interface 59 of programmer 40, forexample, a user creates a stimulation field between a first electrodecarried by the housing of the electrical stimulator, e.g., caseelectrode 520, and a second and third electrodes carried by one or moreimplantable leads, e.g., leads 502, 510, coupled to the housing (700).In this arrangement, the system is configured to perform in a unipolarstimulation arrangement. The user may then use user interface 59 tocreate an anodal shield zone, e.g., shield zone 578, between a fourthand fifth electrode on the one or more leads (705).

In this arrangement, the system is configured to perform in a dual mode,using aspects of both unipolar stimulation and bipolar/multipolarstimulation. As the user increases the intensity of the shield zone(710), e.g., by sliding indicator 562 along horizontal scroll bar 564,the system automatically reduces the current contribution of the firstelectrode, e.g., case electrode 520 (715). The system may turn off thecurrent contribution of the first electrode when that contribution isinsignificant, i.e., when it falls below a minimum threshold. In thisarrangement, the system is now configured to perform only in abipolar/multipolar arrangement because the case electrode has beenturned off. Thus, the system may be configured in a unipolar stimulationarrangement, transition to a hybrid configuration in which aspects ofboth unipolar stimulation and bipolar/multipolar stimulation are used toprovide an overall effect to a patient, and then finally transition to abipolar/multipolar stimulation configuration. Although the abovedescription begins with a unipolar arrangement and finishes with abipolar/multipolar arrangement, the reverse is also contemplated. Thatis, the system may be configured in a bipolar/multipolar stimulationarrangement, transition to a hybrid configuration in which aspects ofboth unipolar stimulation and bipolar/multipolar stimulation are used toprovide an overall effect to a patient, and then finally transition to aunipolar stimulation configuration.

Various techniques have been described above that substantiallysimultaneously deliver electrical stimulation via one or more electrodeson an implantable medical device (IMD) housing and two or moreelectrodes on one or more leads coupled to the housing. As described indetail above, the one or more housing electrodes may be configured todeliver electrical stimulation and automatically balance stimulationcurrents delivered by two or more lead electrodes to produce validstimulation settings. Such configurations may require fewer electrodespecifications from a user. Similar automatic balancing may be achievedutilizing various other configurations, as will be described in detailbelow.

For example, rather than utilizing one or more housing electrodes toautomatically balance the stimulation currents delivered by two or moreselected (e.g., user selected via lead or zone-based programming asdescribed herein) electrodes on one or more leads as described above,one or more other non-selected electrodes, may be automaticallyconfigured to deliver balancing current. The term “selected” electrodeas described herein refers to an electrode selected by a user to performa specific purpose such as to generate a stimulation field or shieldzone in patient tissue. The term “non-selected” as described hereinrefers to an electrode not selected by a user to perform a specificpurpose.

This disclosure describes delivery of electrical stimulation by at leastone first user-selected electrode and at least one second user-selectedelectrode configured to deliver electrical stimulation and automaticallyselecting, by a programmer, at least one third electrode not selected bythe user to deliver electrical stimulation to substantially balancestimulation delivered by the at least one first and at least one secondelectrode. For example, the at least one third electrode maysubstantially balance the electrical stimulation delivered by the atleast one first and at least one second user-selected electrodes bybalancing at least a portion of the electrical stimulation delivered bythe at least one first and at least one second user-selected electrodes.In some examples, a substantially balancing current delivered by the atleast one third electrode may be substantially equal to a difference incurrent delivered by the at least one first and at least one seconduser-selected electrodes as specified by a user, e.g., such that thebalancing current balances substantially all of the difference incurrent delivered by the at least one first and at least one seconduser-selected electrodes. In other examples, a substantially balancingcurrent may balance a portion of a difference between currents deliveredby the at least one first and at least one second user-selectedelectrodes as specified by a user. The balancing current may be a sinkcurrent or a source current, as appropriate, depending on the polarityof the difference between currents generated by the at least one firstand at least one second user-selected electrodes. In this case, otherportions of the difference may be balanced by one or more additionalthird electrodes.

In some examples, it may be desirable for a balancing current deliveredby the non-selected electrode to be sub-threshold current, i.e., energy(e.g., current, voltage) delivered at amplitude levels below a thresholdat which stimulation can be perceived by a patient. It may be desirableto maintain a charge density of energy delivered by the non-selectedelectrodes at a lower level than a charge density of energy delivered ator above a threshold in which stimulation may be perceived by thepatient. In some examples, balancing currents delivered by the one ormore non-selected electrodes may be automatically configured to deliverenergy selected to not exceed a charge density in which stimulation maybe perceived by the patient. For example, the balancing currentsdelivered by the one or more non-selected electrodes may beautomatically configured to deliver energy below one or morepre-determined thresholds. In other examples, balancing currentsdelivered by the one or more non-selected electrodes may be activelymonitored to ensure that balancing currents do not exceed a chargedensity in which stimulation may be perceived by the patient.

A patient's perception threshold is a current and/or voltage amplitudeat which the patient begins to experience or feel the effects caused bythe electrical stimulation being delivered by one or more electrodes.Example effects caused by the electrical stimulation current includereduction of a symptom, e.g., reduction in chronic pain, andparesthesia. In some examples, the perception threshold for each patientmay be established via testing, e.g., in a clinical setting. In otherexamples, the perception threshold may be based on a model, e.g., abasic body model, defined by a patient's age, sex, weight, and the like.The phrase “sub-threshold current” is used throughout this disclosure todescribe electrical stimulation current having an amplitude below apatient's perception threshold. Utilizing non-selected lead electrodesrather than housing (i.e.) electrodes to balance stimulation current maybe desirable. For example, stimulation configurations that utilize oneor more housing electrodes to deliver stimulation current may causeadditional heating or other undesirable effects when an IMD is exposedto external conditions, such as when a patient is in a magneticresonance imaging (MRI) machine. In addition, stimulation configurationsthat utilize one or more housing electrodes to deliver stimulationcurrent may deliver current above a patient's perception threshold,e.g., in a subcutaneous pocket in which IMD 4 is implanted.

By utilizing one or more lead electrodes to balance the stimulationcurrent, balancing may be achieved while minimizing undesirable inducedcurrents when a patient walks through a theft detection or airportsecurity device. In addition, an IMD may be less likely to unnecessarilyheat when influenced by external interference from a magnetic resonanceimaging MRI procedure.

In various examples, a patient's perception threshold may be apredetermined threshold. The predetermined threshold may indicate acurrent level at which a patient is expected to perceive delivery of theelectrical stimulation current. In one example, a predeterminedthreshold of one or more electrodes may be identified based on userinput indicating a patient response to electrical stimulation deliveredvia the one or more electrodes. In some examples, the predeterminedthreshold may be tissue specific, e.g., a perception threshold for aparticular region of patient tissue, or may be electrode or electrodecombination specific, e.g., based on user perception of electricalstimulation delivered by the particular electrode or combination ofelectrodes. In other examples, a predetermined threshold may be ageneral value for which a plurality of electrodes disposed in proximityto different regions of patient tissue do not cause a perceived responsein patient tissue. Again, the phrase “sub-threshold” as used in thisdisclosure refers to the delivery of electrical stimulation currentbelow a patient's perception threshold

FIGS. 30-32 are conceptual diagrams illustrating example lead andelectrode configurations that may be used for delivering electricalstimulation therapy according to various techniques of this disclosure.FIG. 30 is similar to the configuration depicted in FIG. 15. FIG. 30depicts two leads 300, 340, with lead 300 comprising lead body 306having four electrodes 304 (electrodes 304A-304D) mounted at variouslengths of lead body 306, and lead 340 comprising lead body 342 havingfour electrodes 344 (electrodes 344A-344D) mounted at various lengths oflead body 342. Unlike the configuration of FIG. 15, which uses housingelectrode 13 on IMD 4 to deliver electrical stimulation to balance thestimulation currents delivered by two or more electrodes on leads 300,340, non-selected lead electrodes of FIG. 30, e.g., lead electrodes thatwere not specifically targeted by a user as having a specific purpose,e.g., electrodes used for stimulation or shielding, may be automaticallyturned on (in some examples below a patient's perception threshold), inorder to balance the stimulation and/or shielding currents delivered byelectrodes selected for a specific purpose (e.g., stimulation orshielding). In other words, in the configuration depicted in FIG. 30,any lead electrode not specifically selected by a user for stimulationor shielding may be automatically configured to deliver balancingcurrents, rather than the using the housing electrode, e.g., housingelectrode 13, to deliver balancing currents as set forth above. In otherexamples, as described in further detail below, the one or morenon-selected electrodes may be automatically selected to deliver abalancing current to compensate for a user initiated change in astimulation program, e.g., user selection of a different electrodecombination for the delivery of shield or stimulation, or usermodification of stimulation currents delivered by user selectedelectrodes. In still other examples, a user may be provided with anability to switch between delivery of balancing currents via one or morenon-selected lead electrodes and a housing electrode of an IMD. A usermay further be provided with an ability to select relative contributionsof one or more non-selected lead electrodes and a housing electrode ofan IMD.

Referring to the example of FIG. 30, a first stimulation field (notshown) may be produced when electrode 304D is configured to act as ananode and source current, and electrode 304C is configured to act as acathode and sink the current sourced by electrode 304D. A secondstimulation field may be produced when electrode 344D is configured toact as an anode and source current and electrode 344C is configured toact as a cathode and sink the current sourced by electrode 344D. Asdescribed previously in this disclosure, the currents used to producethe first stimulation field and the second stimulation field (e.g.,currents selected by a user) may not be equal and, as such, the systemmay need to deliver additional electrical stimulation current in orderto balance the net charges delivered to the patient. Rather thanautomatically configuring housing electrode 13 to deliver the electricalstimulation current needed for balancing, one or more of lead electrodes304A, 304B, 344A, and 344B may be used to deliver the balancing current.That is, because a user has not specifically targeted lead electrodes304A, 304B, 344A, and 344B as having a specific purpose, e.g.,stimulation or shielding, lead electrodes 304A, 304B, 344A, and 344B areavailable to automatically, i.e., without user intervention, be causedto deliver a third electrical stimulation current to balance the firstand second currents delivered by user selected electrodes 304C, 304D,344C and 344D. In some examples, balancing currents delivered bynon-selected electrodes 304A, 304B, 344A, and 344B may be selected tohave amplitudes below a patient's perception threshold, i.e.,sub-threshold current, substantially simultaneously with the currentsdelivered to produce the first and second electrical fields in order tobalance the total amount of current delivered (sourced and sunk).

By way of specific example, patient 6 may desire electrical stimulationtherapy that requires a stimulation current of about 5 mA. Patient 6 mayfirst select one or more cathodes, e.g., electrodes 304C, 344C on leadbodies 306, 342, respectively, to deliver (sink) cathodal current, e.g.,5 mA to produce a stimulation region. Patient 6 may also select one ormore anodes, e.g., electrodes 304D, 344D on lead bodies 306, 342,respectively, to deliver (source) anodal current, e.g., 3 mA to producean anodal shield. One or more non-selected electrodes on leads 300, 340may then be automatically configured as anodes to deliver (source)current in order to balance the remaining current requirement, e.g., 2mA. That is, one or more of non-selected electrodes 304A, 304B, 344A,and 344B may be automatically recruited as balancing electrodes todeliver (source) the remaining current required to balance the anodaland cathodal currents delivered by electrodes 304C, 304D, 344C, and344D, e.g., 2 mA.

For example, each of non-selected electrodes 304A, 304B, 344A, and 344Bmay be automatically recruited by IMD 4 to deliver (source) 2 mA ofcurrent to provide the remaining 2 mA required for balancing (e.g., 0.5mA per non-selected electrode). Or, rather than dividing the remainingcurrent equally between non-selected electrodes 304A, 304B, 344A, and344B, the current required to balance the system may be dividedunequally. For example, it may be desirable for the electrodes that arefurthest away from the electrodes producing stimulation or shields tosource more sub-threshold current than electrodes that are closer to theelectrodes producing stimulation or shields. In some examples, all ofthe sub-threshold current collectively delivered by non-selectedelectrodes 304A, 304B, 344A, and 344B may equal a current sufficient tobalance currents of selected electrodes 304C, 304D, 344C, and 344D.

In FIG. 30, electrodes 304A and 344A are furthest away from theelectrodes used to produce stimulation or shields (electrodes 304C,304D, 344C, 344D). As such, electrodes 304A and 344A may beautomatically configured to each deliver (source) 0.8 mA, whileelectrodes 304B and 344B are automatically configured to deliver(source) 0.2 mA. The current amplitude of 0.8 mA may be sub-thresholdfor the purposes of explanation. In this manner, the remaining 2 mArequired to balance the currents delivered (sourced and sunk) to thepatient via non-selected electrodes, with the electrodes furthest awayfrom the electrodes used for producing stimulation fields delivering themost balancing current.

In one example, it may be desirable to utilize electrodes having greatersurface areas for delivering balancing current. As mentioned above, itmay be desirable to minimize the charge density beneath the non-selectedelectrodes. Non-selected electrodes with greater surface areas maydeliver more current at the same or lower charge density than othernon-selected electrodes with smaller surface areas. For example, a firstnon-selected electrode having twice the surface area of a secondnon-selected electrode may deliver electrical stimulation current havingtwice the current amplitude and the same current density as the secondnon-selected electrode. As such, the first non-selected electrode may bedesirable because it can be used to deliver more current while remainingat an acceptable charge density level. In some examples, each surfacearea of each electrode within a lead configuration may be stored withinmemory 52 (or memory 55), for example. Then, based on the surface areaof an electrode, processor 50 (or processor 53) may determine the amountof current that the electrode may deliver while remaining substantiallysub-threshold.

It should be noted that although FIG. 30 depicts two leads, namely leads300, 340, a single lead, or more than two leads, may be also used toperform the techniques of this disclosure. That is, a single lead, ormore than two leads, may include electrodes that may be automaticallyconfigured to deliver balancing current substantially simultaneouslywith current delivered one or more user-selected electrodes.

Further, it should be noted that additional electrodes implanted withinthe body of patient 6 might also be used as non-selected electrodes todeliver balancing current. For example, additional electrodes on leadsimplanted within subcutaneous pockets of patient 6 may be automaticallyconfigured to deliver balancing current in the manner described in thisdisclosure. Patient 6 may have one or more leads having one or moreelectrodes implanted within one or more subcutaneous pockets in his/herback. In some examples, these leads and electrodes may be dedicated fordelivery of balancing current. In other examples, these leads andelectrodes may be used primarily for other electrical stimulationtherapy purposes, but may be recruited by IMD 4 to deliver balancingcurrent if the electrodes are not being fully utilized for their primaryelectrical stimulation purpose.

FIG. 31 is a conceptual diagram illustrating another example lead andelectrode configurations that may be used for delivering electricalstimulation therapy according to various techniques of this disclosure.FIG. 31 depicts a 2×8 electrode configuration (two leads, e.g., leads502, 510, with eight electrodes each) used to produce stimulation zone576 and anodal shield zone 578. Stimulation zones and anodal shieldzones may be referred to collectively as stimulation fields. Electrodes528B, 528I, and 528J are used to produce stimulation zone 576 andelectrodes 528C and 528K are used to produce anodal shield zone 578.Electrodes 528B, 528I, and 528J deliver (sink) 11.30 mA, 8.47 mA, and1.513 mA, respectively. Electrodes 528C and 528K deliver (source) 9.87mA and 14.58 mA, respectively. In other words, electrodes 528C and 528Kdeliver first electrical stimulation current with a first polarity, andelectrodes 528B, 528I, and 528J deliver second electrical stimulationcurrent with a second polarity opposite the first polarity. Each of thecurrents used to produce stimulation zone 576 and anodal shield zone 578may be above a patient's perception threshold, i.e., not sub-thresholdcurrents.

It is readily seen that the total current sunk (34.9 mA) by electrodes528B, 528I, and 528J does not equal the total current sourced (24.45 mA)by electrodes 528C and 528K. In other words, the total current sunk isnot balanced by the total current sourced for the electrodes selected bythe user. In order to balance the currents used to produce stimulationzone 576 and anodal shield zone 578, and thus the net charge deliveredby the system, one or more electrodes not selected to producestimulation fields, e.g., stimulation zone 576 and anodal shield zone578, may be automatically configured to deliver (source), at asub-threshold level, the remaining (anodal) current (10.45 mA) requiredfor balancing.

There are numerous ways to determine which non-selected electrode(s) toautomatically configure to deliver a balancing current. In one example,processor 50 may simply determine candidate electrodes for the deliveryof balancing current based on whether or not the electrodes wereselected by the user for the delivery of current for purposes ofstimulation or shielding (user-selected electrodes). In another example,processor 50 may determine candidate electrodes for the delivery ofbalancing current by selecting those electrodes which were not userselected, and that are also not adjacent to user-selected electrodes. Instill other examples, processor 50 may determine candidate electrodesfor the delivery of balancing current by selecting those electrodeswhich were not user selected, and that are also not adjacent to anyuser-selected electrodes configured to deliver current of an oppositepolarity. In still another example, processor 50 may determine candidateelectrodes for the delivery of balancing current by first selecting afirst electrode furthest away from any selected electrode to deliver apredetermined percentage of a desired balancing current (e.g., 10%),then select the next non-selected electrode furthest away from anyuser-selected electrode to deliver the predetermined percentage, and soon, until the remaining amount of desired balancing current is to bedelivered.

As mentioned above, it may be desirable to utilize the electrodes thatare furthest away from any stimulation or anodal shield zones. Electrode528A is an electrode adjacent to stimulation zone 576 and, as such, maybe less desirable than other electrodes 528 for delivering balancingcurrent. If electrode 528A were used to deliver balancing current, thecurrent it delivered might undesirably affect stimulation zone 576 andthus the electrical stimulation therapy delivered to patient 6.

In the configuration depicted in FIG. 31, electrodes 528D-528H andelectrodes 528L-528P have been automatically configured to deliverbalancing current. Each of these electrodes have not been user selectedto deliver stimulation or shield currents. Although electrodes 528D and528K are adjacent anodal shield zone 578, these electrodes are notnecessarily undesirable for the delivery of balancing current becausethe polarity of the sub-threshold current delivered by electrodes 528Dand 528K is the same as the polarity of anodal shield zone 578. Also,with respect to stimulation zone 576, electrodes 528D and 528K are“behind” anodal shield zone 578. As such, electrodes 528D and 528K areunlikely to affect stimulation zone 576. As seen in FIG. 31, thebalancing current delivered by each of electrodes 528D-528H andelectrodes 528L-528P is equal (1.05 mA). These ten electrodes deliver atotal of 10.50 mA of current, thereby balancing the total chargedelivered by the system: 24.45 mA+10*(1.045 mA)=34.9 mA.

FIG. 32 is a conceptual diagram illustrating another example lead andelectrode configuration that may be used for delivering electricalstimulation therapy according to various techniques of this disclosure.The configuration depicted in FIG. 32 is similar to the configurationdepicted in FIG. 31. However, in contrast to FIG. 31, the balancingcurrents depicted in FIG. 32 are not distributed equally amongst thenon-selected electrodes, and electrodes adjacent anodal shield zone 578have not been recruited to deliver balancing current. As describedabove, it may be desirable for electrodes furthest away from stimulationzones and anodal shield zones to deliver more sub-threshold current thanelectrodes that are closer to these zones. For example, in FIG. 32,electrodes 528H and 528P on leads 502, 510, respectively, are thefurthest away from stimulation zone 576 and anodal shield zone 578. Assuch, it may be desirable to deliver a higher amount of balancingcurrent via electrodes 528H and 528P than via electrodes 528E-528G and528M-528O. Similarly, electrodes 528G and 528O may deliver a higheramount of balancing current than that delivered by electrodes 528E-528Fand 528M-528N, and so on.

In FIG. 32, depending on the proximity of the non-selected electrode toa stimulation or anodal zone, the balancing currents delivered decreaselinearly along the length of leads 502, 510 from electrode 528H toelectrode 528E and electrode 528P to electrode 528L (stepping atapproximately 0.52 mA between electrodes on a lead). It should be notedthat in other example configurations, the balancing currents deliveredby the non-selected electrodes may change along a lead in a non-linearmanner. For example, electrodes 528H, 528P may deliver balancing currentthat may be a factor of two greater than the balancing current deliveredby electrodes 528G, 528O. Similarly, electrodes 528G, 528O may deliverbalancing current that may be a factor of two greater than the balancingcurrent delivered by electrodes 528F, 528N, and so on. Of course, afactor of two is used for the purposes of explanation. Other non-linearexamples are within the scope of the disclosure.

Table 1 presented below depicts various example non-selected electrodecurrent combinations that may be used to deliver current required tobalance the system. Table 1 merely represents some combinations ofbalancing currents that may be delivered via one or more non-selectedelectrodes. The examples of balancing currents described in Table 1 areselected to balance a difference in anodic and cathodic currents of10.45 mA between user-selected electrodes 528B-C, and 528I-J. Othercombinations are contemplated and consistent with this disclosure.Further, the specific current levels depicted in Table 1 are withreference to FIGS. 31 and 32 and are merely provided for purposes ofexplanation. Various other current levels are also contemplated andconsistent with this disclosure.

TABLE 1 Non-Linear Relatively Linear Away Away From Equally Equally FromSelected Above-Selected Electrode Distributed Distributed ElectrodesElectrodes 528A +0.95 Not used Not used +.1 528B NA NA NA NA 528C NA NANA NA 528D +0.95 +1.04 Not used +.17 528E +0.95 +1.04  +.52 +.34 528F+0.95 +1.04 +1.04 +.68 528G +0.95 +1.05 +1.56 +1.36 528H +0.95 +1.05+2.08 +2.68 528I NA NA NA NA 528J NA NA NA NA 528K NA NA NA NA 528L+0.95 +1.04 Not used +.16 528M +0.95 +1.04  +.52 +.35 528N +0.95 +1.05+1.04 +.67 528O +0.95 +1.05 +1.56 +1.35 528P +0.95 +1.05 +2.08 +2.67

Column 1 of Table 1 shows electrodes 528A-528P as depicted in FIGS. 31and 32. As depicted in the second column from the left in Table 1(titled “Equally Distributed”), in one example configuration, balancingcurrents may be delivered (sourced) equally amongst non-selectedelectrodes 528A, 528D-528H and 528L-528P. In contrast to theconfiguration depicted in FIG. 31 (which corresponds with the thirdcolumn of Table 1), all electrodes, including electrode 528A that isadjacent stimulation zone 576, that are not being used to producestimulation zone 576 and anodal shield zone 578 have been automaticallyconfigured to deliver (source) the approximately 10.45 mA of currentrequired to balance the system.

The third column from the left in Table 1 (titled “Relatively EquallyDistributed,”) depicts the example configuration shown in FIG. 31. FIG.31 was described in detail above and will not be described again. Thedifference between the second and third columns in Table 1 is the use ofelectrode 528A. Although not as desirable to use for deliveringbalancing current as the remaining electrodes (due to its proximity tostimulation zone 576), in some instances, electrode 528A may nonethelessbe recruited to deliver balancing current.

The fourth column from the left in Table 1 (titled “Linear Away FromAbove-Threshold Electrodes”), depicts the example configuration shown inFIG. 32. FIG. 32 was described in detail above and will not be describedagain. One difference between the third and fourth columns in Table 1 isthat two more electrodes in the fourth column, namely electrodes 528Dand 528L (adjacent anodal shield zone 578), have not been used fordelivering balancing currents. Another difference between the third andfourth columns in Table 1 is that the currents are not distributedequally between the electrodes being used to deliver balancing currents.Rather, as seen in the fourth column and as described above with respectto FIG. 32, the electrodes that are furthest away from stimulation zone576 and anodal shield zone 578 deliver the highest amount of balancingcurrent. The balancing current delivered decreases linearly fromelectrodes 528H, 528P to electrodes 528E, 528M, depending on thedistance between the non-selected electrode and the user-selectedelectrodes used to produce stimulation zone 576 and anodal shield zone578. In one example, the distance between the non-selected electrode andselected the electrodes used to produce stimulation zone 576 and anodalshield zone 578 may be based on a physical dimension. In anotherexample, the distance may be based on a number of electrodes between thenon-selected electrode and the selected electrodes used to producestimulation zone 576 and anodal shield zone 578. The balancing electrodestimulation arrangement described with respect to the fourth column ofTable 1 may be desirable because, by delivering the majority ofbalancing current via the furthest-away electrodes in relation tostimulation zone 576 and anodal shield zone 578, the sub-thresholdcurrent is less likely to interfere with or affect stimulation zone 576and anodal shield zone 578.

The fifth column from the left (or first column from the right) in Table1 (titled “Non-Linear Away From Above-Threshold Electrodes”), a currentdelivered by non-selected electrodes may increase according to anon-linear (e.g., exponential) relationship depending on the distancebetween the non-selected electrode and stimulation zone 576 and anodalshield zone 578. Like in the configuration depicted in column 1, theconfiguration in column 5 utilizes all electrodes 528 that are not usedto produce stimulation zone 576 and anodal shield zone 578, includingelectrode 528A. As shown in the fifth column of Table 1, electrode 528Adelivers a balancing current of 0.1 mA, a relatively low value incomparison with the other balancing currents due to its proximity tostimulation zone 576. Electrode 528D (the closest non-selected electrodeon lead 502 to anodal shield zone 578) is also configured to deliver arelatively small amount of current (0.17 mA). Electrode 528E (the nextclosest non-selected electrode on lead 502 to anodal shield zone 578),is configured to deliver a current approximately twice the amount ofdelivered by electrode 528D (0.34 mA). Similarly, electrode 528F isconfigured to deliver a current approximately twice the amount deliveredby electrode 528E (0.68 mA), and electrode 528G is configured to deliverapproximately twice the amount of current delivered by electrode 528F(1.36 mA). Finally, electrode 528H, the furthest non-selected electrodeon lead 502 from anodal shield zone 578, is configured to deliverapproximately twice the amount of current delivered by non-selectedelectrode 528G (2.68 mA).

Similarly, electrode 528L (the closest non-selected electrode on lead510 to anodal shield zone 578) is used to deliver a relatively smallamount of current (0.16 mA). Electrode 528M (the next closestnon-selected electrode on lead 502 to anodal shield zone 578) isconfigured to deliver a current approximately twice the amount ofdelivered by electrode 528L (0.35 mA). Electrode 528N is configured todeliver approximately twice the amount of current delivered by electrode528M (0.67 mA), and electrode 528O is configured to deliverapproximately twice the amount of current delivered by electrode 528N(1.35 mA). Finally, electrode 528P, the furthest non-selected electrodeon lead 510 from anodal shield zone 578, is configured to deliverapproximately twice the amount of current delivered by electrode 528O(2.67 mA). The balancing electrode stimulation arrangement describedwith respect to the fifth column of Table 1 may be desirable because, bydelivering the majority of balancing current via the furthest-awayelectrodes in relation to stimulation zone 576 and anodal shield zone578, the balancing current is less likely to interfere with or affectstimulation zone 576 and anodal shield zone 578.

The examples described above with respect to electrode configurationsdepicted in Table 1 are directed to an IMD that includes a plurality ofsubstantially similar electrodes carried by one or more leads of theIMD. In other examples not depicted in Table 1, the IMD may includeelectrodes that are not substantially similar. For example, a firstelectrode may have a first surface area, while a second electrode mayhave a different surface area than the first surface area. The surfacearea of the electrode may be used by processor 50, for example, todetermine amplitudes of balancing current that may be delivered by theone or more non-selected electrodes. For example, a larger electrodethat presents a larger surface area may deliver more current but at thesame current density than another electrode having a smaller surfacearea. Thus, the size, shape and, in particular, the surface area, of oneor more non-selected electrodes may be taken into account by processor50 in determining relative balancing current contributions of one ormore non-selected electrodes.

It should also be noted that the balancing current electrode techniquesof this disclosure are not limited to non-selected electrodes beingautomatically, i.e., without user intervention, configured as anodes todeliver (source) current required to balance the system. Rather, one ormore non-selected electrode(s) may also be automatically, i.e., withoutuser intervention, configured as one or more cathodes to deliver (sink)current required to balance the system. As described herein, the one ormore non-selected electrodes may be automatically configured as one ormore anodes or cathodes to deliver balancing current by one or moreprocessors. The one or more processors may be a processor of the IMD, ofanother IMD, or of an external programmer or larger IMD system.

FIG. 33 depicts a user interface illustrating an arrangement that makesuse of non-selected electrodes to automatically balance the currentdelivered by the system, in accordance with the techniques describedabove, created using zone-based programming. User interface 59 of FIG.33 depicts the electrode configuration shown and described above withrespect to FIG. 31. FIG. 33 is similar to the user interface shown inFIG. 25 and, as such, user interface 59 will not be described in detailagain. Window 504 of FIG. 33 depicts stimulation zone 576 and anodalshield zone 578. Stimulation zone 576 is produced by electrodes 528B,528I, and 528J delivering (sinking) currents of 8.47 mA, 11.30 mA, and15.13 mA, respectively. Anodal shield zone 578 is produced by electrodes528C and 528K delivering (sourcing) currents of 9.87 mA and 14.58 mA,respectively. As seen in FIG. 33, case electrode 520 is not deliveringany current (0.00 mA).

The total current sunk (34.9 mA) by electrodes 528B, 528I, and 528J doesnot equal the total current sourced (24.45 mA) by electrodes 528C and528K. In other words, the total current delivered by the system is notbalanced. In order to balance the currents used to produce stimulationzone 576 and anodal shield zone 578, and thus the net charge deliveredby the system, one or more electrodes not used to produce stimulationzone 576 and anodal shield zone 578 may be automatically configured todeliver (source) the remaining (anodal) current (10.45 mA in the exampleof 33) required for balancing.

In accordance with the techniques of this disclosure, processor 53 ofprogrammer 40, for example, automatically configures non user-selectedelectrodes 528D-528H and electrodes 528L-528P to deliver balancingcurrent. In some examples, the balancing current may be sub-thresholdcurrent delivered below a patient's perception threshold. Each of thenon-selected electrodes may outside any keep out areas, e.g., an ellipseor other geometric shape “drawn” by processor 53 around electrodes usedto produce stimulation or anodal shield zones. Each of the non-selectedelectrodes may instead be electrodes not directly selected by the userto deliver energy for shielding or stimulation. Although electrodes 528Dand 528K are adjacent anodal shield zone 578, these electrodes are notnecessarily undesirable for delivery of balancing currents because thepolarity of the sub-threshold current delivered by electrodes 528D and528K (positive) is the same as the polarity of anodal shield zone 578(positive). Also, with respect to stimulation zone 576, electrodes 528Dand 528K are “behind” anodal shield zone 578. As such, electrodes 528Dand 528K are unlikely to affect stimulation zone 576. Electrode 528A isan electrode adjacent to stimulation zone 576 and as such, may be lessdesirable than other electrodes 528 for delivering balancing current. Ifelectrode 528A were used to deliver balancing current, it may affectstimulation zone 576 and thus the electrical stimulation therapydelivered to patient 6. Thus, in the configuration shown in FIG. 33,programmer 40 has determined that electrode 528A should not be used todeliver balancing current.

As seen in FIG. 33, the balancing current delivered by each ofelectrodes 528D-528H and electrodes 528L-528P is equal (1.045 mA). Theseten electrodes deliver a total of 10.45 mA of current, thereby balancingthe net charge delivered by the system (24.45 mA+10.45 mA=34.9 mAsourced current). In this manner, non-selected electrodes on leads 502,510 that are not used to produce either stimulation or anodal shieldzones may be used to automatically balance the net current delivered bythe system.

Arrays 572 and 574 depict the contributions of each of the zones on eachof the two leads 502, 510. In order to determine the contributions ofthe non-selected electrodes 528D-528H and non-selected electrodes528L-528P, the current delivered by the selected electrodes is comparedto the contributions by other anodes. As seen in FIG. 33, the tennon-selected electrodes deliver 10.45 mA/14.58 mA, or 0.716. Thus, eachof the ten non-selected electrodes has a contribution of approximately0.07, as seen in arrays 572, 574.

FIG. 34 depicts another user interface illustrating an arrangement thatmakes use of non-selected electrodes to automatically balance thecurrent delivered by the system, in accordance with the techniquesdescribed above, created using zone-based programming. In particular,FIG. 34 depicts an arrangement in which both case electrode 520 and oneor more non-selected electrodes on leads 502, 510 are automaticallyconfigured to balance the net current delivered by the system. In orderto select a balance between case electrode 520 and one or morenon-selected electrodes on leads 502, 510, a user may use a stylus orother pointing media to move indicator 582 along horizontal scroll bar582. For example, in FIG. 34, the balance is set at 0.50, as shown at585. In other words, the percentage of current to be automaticallydelivered by case electrode 520 is equal to the percentage of current tobe automatically delivered by one or more non-selected lead electrodes.

Stimulation zone 576 and anodal shield zone 578 are identical to thosedescribed in FIG. 33 and, as such, will not be described again. Thetotal current sunk (34.9 mA) by electrodes 528B, 528I, and 528J does notequal the total current sourced (24.45 mA) by electrodes 528C and 528K.In order to balance the currents used to produce stimulation zone 576and anodal shield zone 578, and thus the net charge delivered by thesystem, case electrode 520 and one or more electrodes not used toproduce stimulation zone 576 and anodal shield zone 578 may beautomatically configured to deliver (source), at a sub-threshold level,the remaining (anodal) current of 10.45 mA required for balancing.

Based on the balance setting of 0.50 determined via horizontal scrollbar 584, processor 53, for example, divides the required balancingcurrent of 10.45 mA approximately equally between case electrode 520 andone or more non-selected electrodes 528 on leads 502, 510. In otherwords, processor 53 automatically configures case electrode 520 todeliver (source) approximately 5.225 mA and one or more non-selectedelectrodes to deliver (source) the remaining 5.225 mA of current. Asseen in FIG. 34, each of non-selected lead electrodes 528D-528H and528L-528P deliver approximately 0.5225 mA of current. These tenelectrodes deliver a total of 5.225 mA of current, thereby balancing thenet charge delivered by the system along with case electrode 520, whichalso delivers 5.225 mA of balancing current. In this manner,non-selected electrodes on leads 502, 510 that are not used to produceeither stimulation or anodal shield zones may be used in conjunctionwith case electrode 520 to automatically balance the net currentdelivered by the system.

To determine the contribution of case electrode 520, the current sourcedby case electrode 520 is compared to the contributions by other anodes.Thus, case electrode 520 has a contribution of 5.225 mA/14.58 mA, orabout 0.358, as shown at 542. Arrays 572 and 574 depict thecontributions of each of the zones on each of the two leads 502, 510. Inorder to determine the contributions of the non-selected lead electrodes528D-528H and 528L-528P, the current delivered by the non-selectedelectrodes is compared to the contributions by other anodes. As seen inFIG. 34, the ten non-selected electrodes deliver 5.225 mA/14.58 mA, or0.358. Thus, each of the ten non-selected electrodes has a contributionof 0.0358 in arrays 572, 574.

It should be noted that in the example shown in FIG. 34, it may bedesirable for only electrodes 528G, 528H, 528O, and 528P to deliver theremaining 5.225 mA of current. These four electrodes are the furthestaway from stimulation zone 576 and anodal shield zone 578 and, as such,would have the least effect on zones 576, 578. Or, it may be desirableto configure the non-selected electrodes along leads 502, 510 to deliverthe balancing currents in a non-linear manner, as described above. Theconfiguration shown in FIG. 34 is only one of many possibleconfigurations that may be used to automatically balance the net currentdelivered by the system.

FIG. 35 depicts another user interface presented by the programmer ofFIG. 4 that may be used to automatically balance the current deliveredby the system, created using zone-based programming. In particular FIG.35 depicts the configuration shown in FIG. 34, but with the balancebetween non-selected electrodes and the case electrode at 1.0, as shownat 585. In other words, all current required to balance the currentsdelivered by the system will be delivered by case electrode 520, andnon-selected electrodes on leads 502, 510 will not be used. The userinterface of FIG. 35 is similar to the configuration shown and describedabove with respect to FIG. 25 and, as such, will not be described again.It should be noted that if indicator 582 was moved completely to theleft on horizontal scroll bar 584, the system would be configured todeliver all balancing currents via one or more non-selected electrodes,as shown in FIG. 33.

As mentioned above, utilizing lead electrodes rather than housingelectrodes to balance stimulation current may be desirable to reduce oreliminate additional heating in the case electrode during an MRIprocedure, as well as to reduce or eliminate EMI issues when utilizingthe case electrode to deliver some or all of the balancing current. Theconfigurations depicted in FIGS. 34 and 35 allow a user to easilytransition between case electrode based delivery of balancing currentand non-selected lead electrode based delivery of balancing current, aswell as hybrids utilizing both aspects. For example, a patient who isabout to be imaged in an MRI modality may transition to the non-selectedelectrode based configuration shown in FIG. 33. Or, if a patient isexperiencing undesirable stimulation via the case electrode, e.g., in asubcutaneous pocket, when the case electrode is delivering all of thebalancing current, then the patient may adjust the balance (usinghorizontal scroll bar 584) to deliver some or all balancing current vianon-selected electrodes on leads 502, 510.

FIG. 36 depicts another user interface illustrating an arrangement thatmakes use of non-selected electrodes to automatically (e.g., withoutuser intervention, such as by one or more processors) balance thecurrent delivered by the system, in accordance with the techniquesdescribed above, created using electrode-based programming. Rather thanutilizing zone-based programming for automatically configuringnon-selected electrodes, as in the configurations shown in FIGS. 33-35,electrode-based programming may be utilized. Electrode-based programmingwas described in detail above with respect to FIGS. 18-21 and, as such,will not be described in detail again.

FIG. 36 is similar to FIG. 20, with the notable exception that one ormore non-selected electrodes, rather than the case electrode, areconfigured to automatically deliver balancing current. After a user hasselected the particular electrodes 528 to create stimulation zone 526and anodal shield zone 544 and selected the desired intensity, processor53 of programmer 40 generates fields 526, 546 and depicts the currentsassociated with the selected electrodes that are needed to generatefields 526, 546. As shown in FIG. 36, electrodes 528D and 528L,configured as anodes, each source 3.25 mA and 3.25 mA (a total of 6.5mA). Electrodes 528C and 528K, configured as cathodes, sink 4.88 mA and6.51 mA (a total of 11.39 mA), respectively. The remaining currentneeded to balance the system, 4.89 mA, is entirely sourced by one ormore non-selected electrodes 528 on leads 502, 510, as selected by theuser by sliding indicator 582 to the left along horizontal scroll bar584. Although there are numerous methods to distribute the currentbetween electrodes on leads 502, 510 that are not being used to producestimulation zone 526 and anodal shield zone 544, window 504 depicts thecurrents being equally distributed between the four electrodes furthestaway from zones 526, 544. In particular, electrodes 528G, 528H, 528O,and 528P each deliver 1.2225 mA of current, or a total of 4.89 mA. Inthis manner, electrode-based programming may be used to automaticallybalance the currents delivered by the system.

Arrays 538, 540 depict the contributions of each of the electrodes oneach of the two leads 502, 510. In order to determine the contributionsof the non-selected lead electrodes 528G, 528H, 528O, and 528P, thecurrent delivered by the non-selected lead electrodes is compared to thecontributions by other anodes. As seen in FIG. 36, the four non-selectedelectrodes deliver 4.89 mA/6.50 mA, or 0.752. Thus, each of the fournon-selected electrodes has a contribution of 0.1878 as shown in arrays538, 540.

Although user interface 59 of FIG. 36 depicts non-selected electrodesdelivering all of the balancing current, as determined by the positionof indicator 582, it should be noted that the balancing current may bedivided between case electrode 520 and one or more non-selectedelectrodes on leads 502, 510 in a manner similar to that described abovewith respect to FIGS. 34 and 35.

FIG. 37 is a flow diagram illustrating example operation of a programmerfor generating a program to control delivery of electrical stimulation.In FIG. 37, a programmer, e.g., external programmer 40, receives, viauser interface 59, user input specifying an electrode combination fordelivery of electrical stimulation from an electrical stimulator to apatient (800). The electrode combination may comprise two or moreelectrodes selected by a user to deliver electrical stimulation for aparticular purpose, i.e., two or more electrodes configured to produceone or more stimulation zones and/or anodal shield zones. The two ormore electrodes may be selected from a plurality of electrodes carriedby at least one lead of the IMD (e.g., leads 502, 510). Programmer 40determines at least one non-selected electrode to deliver electricalstimulation to automatically balance the net current delivered by thesystem (805). In one example, programmer 40 automatically determines thenon-selected electrode(s) based on the two or more electrodes configuredto produce one or more stimulation zones and/or anodal shield zones. Forexample, programmer 40 may determine one or more keep out areas andselect non-selected electrodes based on their proximity to the keep outareas. In some examples, the amount of current delivered via eachnon-selected electrode may increase linearly along the length of a leadsuch that electrodes furthest away from stimulation zones and/or anodalshield zones deliver the most balancing current of the non-selectedelectrodes. In other examples, the current delivered via eachnon-selected electrode may increase in a non-linear manner. Programmer40 may then define an electrical stimulation program to deliverelectrical stimulation by the stimulator based at least in part on theuser input specifying the selected electrode combination (810).

The non-selected electrodes may be carried by the same lead(s) used toproduce cathodic stimulation zones and/or anodal shield zones, or bydifferent leads located in other regions of a patient's body, e.g., asubcutaneous pocket in the patient's back. In some examples, thestimulation zones may deliver (sink) more current than the anodal shieldzones deliver (source). As such, non-selected electrodes may beconfigured as cathodes to deliver (sink) additional current required tobalance the net current delivered by the system. In another example, thestimulation zones may deliver (sink) less current than the anodal shieldzones deliver (source). As such, the non-selected electrodes may beconfigured as anodes to deliver (source) additional current required tobalance the net current delivered by the system.

In some examples, specifying an electrode combination comprises using apointing media, e.g., a stylus, to select electrodes of the electrodecombination. In other examples, specifying an electrode combinationcomprises dragging a stimulation field, e.g., stimulation zone or anodalshield zone, relative to the one or more leads. The user mayadditionally add and drag another stimulation field relative to the atleast one lead.

FIG. 38 is a flow diagram illustrating an example method of deliveringelectrical stimulation using the techniques of this disclosure. In themethod shown in FIG. 38, IMD 4, and in particular, stimulation generator60, delivers first electrical stimulation current with a first polarity(e.g., negative) via a first electrode of IMD 4, e.g., electrode 304C ofFIG. 30, (900). The electrical stimulation current delivered by thefirst electrode may have an amplitude above a patient's perceptionthreshold. Stimulation generator 60 delivers second electricalstimulation current with a second polarity opposite the first polarity(e.g., positive) via a second electrode, e.g., electrode 304D of FIG.30, (905). The electrical stimulation current delivered by the secondelectrode may have an amplitude above the patient's perceptionthreshold. The electrical stimulation current delivered by the first andsecond electrodes is used to produce cathodic stimulation zones and/oranodal shield zones. Without user intervention, stimulation generator 60delivers third electrical stimulation via at least one third electrodeof IMD 4, e.g., electrode 304A, that is not configured to produce astimulation field, i.e., an electrode that is not user selected toproduce a stimulations zone and/or an anodal shield zone (910).Stimulation generator 60 delivers the third electrical stimulationcurrent substantially simultaneously with the electrical stimulationcurrent delivered via the first electrode and the second electrode. Insome examples, the third electrical stimulation current has an amplitudebelow a perception threshold. In other words, the third electrode may beconfigured to deliver sub-threshold current. In this manner, stimulationgenerator 60 automatically configures the third electrode to deliver adifference in current between the first electrical stimulation currentand the second electrical stimulation current, thereby automaticallybalancing the net charge delivered by the system.

In some examples, stimulation generator 60A may couple the firstelectrode, e.g., electrode 304C, to a first regulated current path todeliver a first amount of the electrical stimulation current.Stimulation generator 60A may also couple the second electrode, e.g.,electrode 304D, via switch array 66, to a second regulated current pathto deliver a second amount of the electrical stimulation current.Stimulation generator 60A may couple the third electrode, e.g.,electrode 304A, to a regulated current path to receive a third amount ofthe electrical stimulation current. The third amount of electricalstimulation current may be approximately equal to a sum of the first andsecond amounts of the electrical stimulation current. In one example,the first amount of the electrical stimulation current is a firstregulated source current, the second amount of the electricalstimulation current is a second regulated source current, and the thirdamount of the electrical stimulation current is a regulated sink currentthat is approximately equal to a sum of the first and second regulatedsource currents.

Numerous other configurations are considered to be within the scope ofthis disclosure. Such configurations may include, but are not limited tothe following examples. One example configuration delivers (sources)regulated current via the third electrode, delivers (sources) regulatedcurrent via the first electrode, and delivers (sinks) regulated currentvia the second electrode.

Another example configuration delivers (sources) regulated current viathe third electrode, delivers (sources) regulated current via the firstelectrode, and delivers (sinks), via the second electrode, unregulatedcurrent to a reference voltage. That is, the second electrode iselectrically coupled to a reference voltage to deliver (sink)unregulated current.

Another example configuration delivers (sources) regulated current viathe third electrode, delivers (sources) regulated current via the firstelectrode, and delivers, via the second electrode, unregulated current(sources) from a reference voltage. That is, the second electrode iselectrically coupled to a reference voltage to deliver (source)unregulated current.

Another example configuration delivers (sinks), via the third electrode,unregulated current, to a reference voltage (i.e., the third electrodeis electrically coupled to a reference voltage to deliver (sink)unregulated current), delivers regulated current (sources) via the firstelectrode on a lead, and delivers (sources) regulated current via thesecond electrode.

Another example configuration delivers (sources), via the firstelectrode, unregulated current, from a reference voltage (i.e., thefirst electrode is electrically coupled to a reference voltage todeliver (sources) unregulated current), delivers regulated current(sources) via the first electrode, and delivers (sinks) regulatedcurrent via the second electrode.

Another example configuration delivers (sinks), via the third electrode,unregulated current, to a reference voltage (i.e., the third electrodeis electrically coupled to a reference voltage to deliver (sink)unregulated current), delivers (sources), from a regulated voltagesource, unregulated current via the first electrode, and delivers(sinks), to a regulated voltage source, unregulated current via thesecond electrode.

Another example configuration delivers (sources), via the thirdelectrode, unregulated current, from a reference voltage (i.e., thethird electrode is electrically coupled to a reference voltage todeliver (sources) unregulated current), delivers (sources), from aregulated voltage source, unregulated current via the first electrode ona lead, and delivers (sinks), to a regulated voltage source, unregulatedcurrent via the second electrode.

FIG. 39 is a flow diagram illustrating another example operation of theprogrammer for generating a program to control delivery of electricalstimulation. FIG. 39 depicts an example in which stimulation isautomatically balanced after a user adjusts one or more aspects ofstimulation, e.g., a change in one or more electrode contributions, achange in the intensity of one or more aspects of a field, or otherchanges that would result in unbalanced stimulation. A user initiatedchange in one or more electrode contributions may include the selectionof an electrode previously not selected as a selected electrode. Aprogrammer, e.g., external programmer 40, may receive a request from auser via user interface 59 to adjust a stimulation field, e.g.,stimulation zone and/or anodal shield zone (1000). In response, theprogrammer, and in particular processor 53, calculates a non-selectedlead electrode contribution (and, in some examples, also a caseelectrode contribution) necessary to balance the change caused by therequested adjustment (1005).

Processor 53 may, for example, compare the calculated non-selectedelectrode contribution with one or more pre-determined threshold valuesin order to determine if the non-selected lead electrode contributioncalculated is achievable (1010). If the non-selected electrodecontribution is not achievable, e.g., the calculated non-selectedelectrode contribution exceeds the threshold value (“NO” at block 1010),then the user is notified, e.g., via user interface 59, that therequested adjustment is not possible (1015). If the calculatednon-selected electrode contribution is achievable, e.g., the calculatednon-selected electrode contribution does not exceed the threshold value(“YES” at block 1010), then the programmer programs the new balancedtherapy to the device (1020). The adjustment requested by the user mayresult, for example, in one or more non-selected lead electrodes (and,in some examples, the case electrode) sourcing more or less current,changing from an anode (source) to a cathode (sink), or turning off,e.g., if the current sourced or sunk by the one or more non-selectedelectrodes after the user adjustment is approximately zero or otherwiseinsignificant. In some examples in which a user initiated change to oneor more electrode contributions may include the selection of anelectrode previously not selected as a selected electrode, theprogrammer may select other non-selected electrodes to balance a currentdelivered by user selected electrodes.

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware or any combination thereof. Forexample, various aspects of the techniques may be implemented within oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), or any other equivalent integrated or discrete logic circuitry,as well as any combinations of such components, embodied in programmers,such as physician or patient programmers, stimulators, or other devices.The terms “processor,” “processing circuitry,” “controller” or “controlmodule” may generally refer to any of the foregoing logic circuitry,alone or in combination with other logic circuitry, or any otherequivalent circuitry, and alone or in combination with other digital oranalog circuitry.

For aspects implemented in software, at least some of the functionalityascribed to the systems and devices described in this disclosure may beembodied as instructions on a computer-readable medium such as randomaccess memory (RAM), read-only memory (ROM), non-volatile random accessmemory (NVRAM), electrically erasable programmable read-only memory(EEPROM), FLASH memory, magnetic media, optical media, or the like. Theinstructions may be executed to support one or more aspects of thefunctionality described in this disclosure.

Various examples of the disclosure have been described. These and otherexamples are within the scope of the following claims.

The invention claimed is:
 1. A method comprising: receiving, via a userinterface of a programmer device for an implantable electricalstimulator, user input specifying at least one first user-selectedelectrode to deliver electrical stimulation of a first polarity and atleast one second user-selected electrode to deliver electricalstimulation of a second polarity different than the first polarity fordelivery of electrical stimulation from an implantable electricalstimulator to a patient; receiving, via the user interface, user inputspecifying amounts of electrical stimulation current to be supplied viathe at least one first user-selected electrode and the at least onesecond user-selected electrode; automatically selecting, by one or moreprocessors, at least one third electrode not specified as auser-selected electrode to deliver electrical stimulation tosubstantially balance the electrical stimulation current to be deliveredvia the at least one first user selected electrode and the at least onesecond user-selected electrode; and defining a program to controldelivery of the electrical stimulation by the stimulator based on theuser input.
 2. The method of claim 1, wherein automatically selectingthe at least one third electrode includes automatically determining anamount of electrical stimulation to be delivered via the at least onethird electrode.
 3. The method of claim 2, wherein automaticallydetermining an amount of electrical stimulation to be delivered via theat least one third electrode includes automatically determining theamount based on a difference between an amount of electrical stimulationdelivered via the at least one first user selected electrode and the atleast one second user-selected electrode.
 4. The method of claim 3,wherein automatically determining an amount of electrical stimulation tobe delivered via the at least one third electrode includes automaticallydetermining the amount equal to the difference between the amount ofelectrical stimulation delivered via the at least one first userselected electrode and the at least one second user-selected electrode.5. The method of claim 3, wherein automatically determining an amount ofelectrical stimulation to be delivered via the at least one thirdelectrode includes automatically determining the amount equal to aportion of the difference between the amount of electrical stimulationdelivered via the at least one first user selected electrode and the atleast one second user-selected electrode.
 6. The method of claim 2,wherein automatically determining an amount of electrical stimulation tobe delivered via the at least one third electrode includes automaticallydetermining a sub-threshold current to be delivered via the at least onethird electrode, and wherein the sub-threshold current comprises acurrent amplitude below a perception threshold of the patient.
 7. Themethod of claim 1, wherein receiving, via the user interface of anelectrical stimulator programmer device, user input specifying the atleast one first user selected electrode and the at least one seconduser-selected electrode comprises: receiving user input via a pointingmedia to select the at least one first user selected electrode and theat least one second user-selected electrode.
 8. The method of claim 1,wherein receiving, via the user interface of an electrical stimulatorprogrammer device, user input specifying the at least one first userselected electrode and the at least one second user-selected electrodecomprises: receiving user input that drags a stimulation field relativeto at least one lead.
 9. The method of claim 1, wherein automaticallyselecting the at least one third electrode includes automaticallyselecting at least one housing electrode.
 10. The method of claim 1,wherein automatically selecting the at least one third electrodeincludes automatically selecting at least one lead electrode.
 11. Themethod of claim 1, wherein automatically selecting the at least onethird electrode comprises automatically selecting at least one leadelectrode and at least one housing electrode.
 12. The method of claim11, further comprising: receiving, from a user, input specifyingrelative contributions of the at least one lead electrode and the atleast one housing electrode to deliver electrical stimulation below theperception threshold of the patient.
 13. The method of claim 12, whereinreceiving, from a user, input specifying relative contributions includesreceiving user input adjusting a slideable medium within a range. 14.The method of claim 1, wherein automatically selecting at least onethird electrode not specified as a user-selected electrode to deliverelectrical stimulation to substantially balance the electricalstimulation current to be delivered via the at least one first userselected electrode and the at least one second user-selected electrodeincludes automatically selecting a plurality of third electrodes. 15.The method of claim 14, wherein automatically selecting a plurality ofthird electrodes includes automatically determining an amount ofelectrical stimulation to be delivered via each of the plurality ofthird electrodes.
 16. The method of claim 14, further comprisingautomatically determining amounts of electrical stimulation to bedelivered via each of the plurality of third electrodes, the amounts ofelectrical stimulation being sub-threshold amounts of current to bedelivered via each of the plurality of third electrodes, wherein thesub-threshold amounts of current comprise sub-threshold currentamplitudes below a perception threshold of the patient.
 17. The methodof claim 14, further comprising automatically determining a respectiveamount of electrical stimulation to be delivered via each of theplurality of third electrodes, the respective amount of electricalstimulation being a respective sub-threshold amount of current to bedelivered via each of the plurality of third electrodes, wherein therespective sub-threshold amounts of current comprise current amplitudesbelow a perception threshold of the patient, and wherein at least someof the respective sub-threshold amounts of current for the plurality ofthird electrodes not equal.
 18. The method of claim 14, wherein theplurality of third electrodes comprises all electrodes not specified asa user-selected electrode.
 19. The method of claim 1, wherein theprogram is a first program, and wherein a first sum of the amounts ofelectrical stimulation current to be supplied via the at least one firstuser-selected electrode and the at least one second user-selectedelectrode and the at least one third electrode substantially equalszero, the method further comprising: receiving, via the user interface,user input specifying an adjustment to at least one of the at least onefirst user-selected electrode and the at least one second user-selectedelectrode; automatically determining, for the at least one thirdelectrode, an amount of electrical stimulation current such that asecond sum of the electrical stimulation currents to be supplied by eachof the first, second, and third electrodes equals zero; and defining asecond program to control delivery of the electrical stimulation by thestimulator based on the automatically determined amounts of electricalstimulation currents.
 20. The method of claim 1, wherein the at leastone third electrode is separated from the at least first user selectedelectrode and the at least one second user-selected electrode by one ormore electrodes not specified to deliver electrode stimulation.
 21. Themethod of claim 1, wherein the at least one third electrode comprisesone or more electrodes furthest away from the at least first userselected electrode and the at least one second user-selected electrode.22. The method of claim 21, wherein the one or more electrodes furthestaway from the at least first user selected electrode and the at leastone second user-selected electrode are lead-based electrodes.
 23. Anon-transitory computer-readable storage medium comprising instructionsthat cause a processor to: receive, via a user interface of a programmerdevice for an implantable electrical stimulator, user input thatspecifies at least one first user-selected electrode to deliverelectrical stimulation of a first polarity and at least one seconduser-selected electrode to deliver electrical stimulation of a secondpolarity different than the first polarity for delivery of electricalstimulation from an implantable electrical stimulator to a patient;receive, via the user interface, user input specifying amounts ofelectrical stimulation current to be supplied via the at least one firstuser-selected electrode and the at least one second user-selectedelectrode; automatically select at least one non user-selected thirdelectrode to deliver electrical stimulation to substantially balance theelectrical stimulation delivered by the at least one first user-selectedelectrode and the at least one second user-selected electrode; anddefine a program to control delivery of the electrical stimulation bythe stimulator based on the user input.
 24. The computer-readablestorage medium of claim 23, wherein the instructions further cause theprocessor to automatically determine an amount of electrical stimulationto be delivered via the at least one non user-selected third electrode.25. The computer-readable storage medium of claim 24, wherein theinstructions cause the processor to automatically determine the amountof electrical stimulation to be delivered via the at least one thirdelectrode based on a difference between an amount of electricalstimulation delivered via the at least one first user-selected electrodeand the at least one second user-selected electrode.
 26. Thecomputer-readable storage medium of claim 24, wherein the instructionscause the processor to automatically determine the amount of electricalstimulation to be delivered via the at least one third electrode equalto a difference between an amount of electrical stimulation deliveredvia the at least one first user-selected electrode and the at least onesecond user-selected electrode.
 27. The computer-readable storage mediumof claim 24, wherein the instructions cause the processor toautomatically determine the amount of electrical stimulation to bedelivered via the at least one third electrode equal to a portion of adifference between an amount of electrical stimulation delivered via theat least one first user-selected electrode and the at least one seconduser-selected electrode.
 28. The computer-readable storage medium ofclaim 24, wherein the instructions cause the processor to automaticallydetermine the amount of electrical stimulation to be delivered via theat least one third electrode to be a sub-threshold current amplitudebelow a perception threshold of the patient.
 29. The computer-readablestorage medium of claim 23, wherein the instructions further cause theprocessor to: receive user input specifying the at least one firstuser-selected electrode and the at least one second user-selectedelectrode based on a user using a pointing media to select the at leastone first user-selected electrode and the at least one seconduser-selected electrode.
 30. The computer-readable storage medium ofclaim 23, wherein the instructions further cause the processor to:receive user input specifying the at least one first user-selectedelectrode and the at least one second user-selected electrode based onuser input that drags a stimulation field relative to at least one lead.31. The computer-readable storage medium of claim 23, wherein theinstructions cause the processor to automatically select the at leastone third electrode that is one or more lead electrodes.
 32. Thecomputer-readable storage medium of claim 23, wherein the instructionscause the processor to automatically select the at least one thirdelectrode that is a housing electrode.
 33. The computer-readable storagemedium of claim 23, wherein the instructions cause the processor toautomatically select the at least one third electrode that is acombination of a housing electrode and at least one lead electrode. 34.The computer-readable storage medium of claim 33, wherein theinstructions cause the processor to receive, from a user, inputspecifying relative contributions of the at least one lead electrode andat least one housing electrode.
 35. The computer-readable storage mediumof claim 34, wherein the instructions cause the processor to receive,from a user, input specifying relative contributions of the at least onelead electrode and the at least one housing electrode includes receivinguser input based on the user adjusting a slideable medium within arange.
 36. The computer-readable storage medium of claim 23, wherein theprogram is a first program, and wherein a first sum of the amounts ofelectrical stimulation current to be supplied via the at least one firstuser-selected electrode and the at least one second user-selectedelectrode and the at least one third electrode substantially equalszero, and wherein the instructions cause the processor to: receive, viathe user interface, user input specifying an adjustment to at least oneof the at least one first user-selected electrode and the at least onesecond user-selected electrode; automatically determine, for the atleast one third electrode, an amount of electrical stimulation currentsuch that a second sum of the electrical stimulation currents to besupplied by each of the first, second, and third electrodes equals zero;and define a second program to control delivery of the electricalstimulation by the stimulator based on the automatically determinedamounts of electrical stimulation currents.
 37. The computer-readablestorage medium of claim 23, wherein the instructions cause the processorto automatically select a plurality of third electrodes not specified asa user-selected electrode to deliver electrical stimulation tosubstantially balance the electrical stimulation current to be deliveredvia the at least one first user selected electrode and the at least onesecond user-selected electrode includes automatically selecting aplurality of third electrodes.
 38. The method of claim 37, wherein theinstructions cause the processor to automatically determine an amount ofelectrical stimulation to be delivered via each of the plurality ofthird electrodes.
 39. A device, comprising: a programmer for animplantable electrical stimulator, the programmer comprising: a userinterface that receives user input that specifies at least one firstuser-selected electrode to deliver electrical stimulation of a firstpolarity and at least one second user-selected electrode to deliverelectrical stimulation of a second polarity different than the firstpolarity for delivery of electrical stimulation from an implantableelectrical stimulator to a patient, wherein the user interface furtherreceives user input specifying amounts of electrical stimulation currentto be supplied via the at least one first user-selected electrode andthe at least one second user-selected electrode; and a processor thatautomatically selects at least one non user-selected third electrode todeliver electrical stimulation to substantially balance the electricalstimulation delivered by the at least one first user-selected electrodeand the at least one second user-selected electrode, wherein theprocessor defines a program to control delivery of the electricalstimulation by the implantable electrical stimulator based on the userinput.
 40. The device of claim 39, wherein the processor furtherautomatically determines an amount of electrical stimulation to bedelivered via the at least one non-user selected third electrode. 41.The device of claim 40, wherein the processor automatically determinesthe amount of electrical stimulation to be delivered via the at leastone non-user selected third electrode based on a difference between anamount of electrical stimulation delivered via the at least one firstuser-selected electrode and an amount of electrical stimulationdelivered via the at least one second user-selected electrode.
 42. Thedevice of claim 40, wherein the processor automatically determines theamount of electrical stimulation to be delivered via the at least onenon-user selected third electrode equal to a difference between anamount of electrical stimulation delivered via the at least one firstuser-selected electrode and an amount of electrical stimulationdelivered via the at least one second user-selected electrode.
 43. Thedevice of claim 40, wherein the processor automatically determines theamount of electrical stimulation to be delivered via the at least onenon-user selected third electrode equal to a portion of a differencebetween an amount of electrical stimulation delivered via the at leastone first user-selected electrode and an amount of electricalstimulation delivered via the at least one second user-selectedelectrode.
 44. The device of claim 40, wherein the processorautomatically determines the amount of electrical stimulation to bedelivered via the at least one third electrode to be a sub-thresholdcurrent amplitude below a perception threshold of the patient.
 45. Thedevice of claim 39, wherein the user interface receives user inputspecifying the at least one first user-selected electrode and the atleast one second user-selected electrode based on a user using apointing media to select the at least one first user-selected electrodeand the at least one second user-selected electrode.
 46. The device ofclaim 39, wherein the user interface receives user input specifying theat least one first user-selected electrode and the at least one seconduser-selected electrode based on user input that drags a stimulationfield relative to at least one lead.
 47. The device of claim 39, whereinthe processor automatically selects the at least one third electrodethat is one or more lead electrodes.
 48. The device of claim 39, whereinthe processor automatically selects the at least one third electrodethat is a housing electrode.
 49. The device of claim 39, wherein theprocessor automatically selects the at least one third electrode that isa combination of at least one lead electrode and at least one housingelectrode.
 50. The device of claim 39, wherein the user interfacereceives, from a user, input specifying relative contributions of the atleast one lead electrode and at least one housing electrode.
 51. Thedevice of claim 50, wherein the user interface receives, from a user,input specifying relative contributions of the at least one leadelectrode and at least one housing electrode includes the user interfacereceiving input based on the user adjusting a slideable medium within arange.
 52. The device of claim 39, wherein the program is a firstprogram, and wherein a first sum of the amounts of electricalstimulation current to be supplied via the at least one firstuser-selected electrode and the at least one second user-selectedelectrode and the at least one third electrode substantially equalszero, and wherein the processor receives, via the user interface, userinput specifying an adjustment to at least one of the at least one firstuser-selected electrode and the at least one second user-selectedelectrode; wherein the processor automatically determines, for the atleast one third electrode, an amount of electrical stimulation currentsuch that a second sum of the electrical stimulation currents to besupplied by each of the first, second, and third electrodes equals zero;and wherein the processor defines a second program to control deliveryof the electrical stimulation by the stimulator based on theautomatically determined amounts of electrical stimulation currents. 53.The device of claim 52, wherein the processor automatically determinesan amount of electrical stimulation to be delivered via each of theplurality of electrodes.
 54. The device of claim 39, wherein theprocessor that automatically selects a plurality of non user-selectedthird electrodes to deliver electrical stimulation to substantiallybalance the electrical stimulation delivered by the at least one firstuser-selected electrode and the at least one second user-selectedelectrode.
 55. A device comprising: means for receiving, via a userinterface of a programmer device for an implantable electricalstimulator, user input that specifies at least one first user-selectedelectrode to deliver electrical stimulation of a first polarity and atleast one second user-selected electrode to deliver electricalstimulation of a second polarity different than the first polarity fordelivery of electrical stimulation from an implantable electricalstimulator to a patient; means for receiving, via the user interface,user input specifying amounts of electrical stimulation current to besupplied via the at least one first user-selected electrode and the atleast one second user-selected electrode; means for automaticallyselecting at least one third electrode to deliver electrical stimulationto substantially balance electrical stimulation delivered by the atleast one first user-selected electrode and the at least one seconduser-selected electrode; and means for defining a program to controldelivery of the electrical stimulation by the stimulator based on theuser input.
 56. A system comprising: an implantable electricalstimulator; and a programmer comprising: a user interface that:receives, via a user interface of a programmer device for an implantableelectrical stimulator, user input that specifies at least one firstuser-selected electrode to deliver electrical stimulation of a firstpolarity and at least one second user-selected electrode to deliverelectrical stimulation of a second polarity different than the firstpolarity for delivery of electrical stimulation from an implantableelectrical stimulator to a patient; receives, via the user interface,user input specifying amounts of electrical stimulation current to besupplied via the at least one first user-selected electrode and the atleast one second user-selected electrode; wherein the programmerautomatically selects at least one third electrode to deliver electricalstimulation to substantially balance electrical stimulation delivered bythe at least one first user-selected electrode and the at least onesecond user-selected electrode; and a processor that defines a programto control delivery of the electrical stimulation by the stimulatorbased on the user input.